Relation of Anthropometric Measures and Indices to Isokinetic Trunk Strength –a Retrospective Analysis
Der Zusammenhang von anthropometrischen Messgrößen mit isokinetischer Rumpfkraft – eine retrospektive Analyse
Summary
Problem: Relations between anthropometric measures and isokinetic trunk strength are known for age, sex, weight and height in a healthy population as well for body mass index (BMI) in an obese population. Limited data exists regarding the interaction with waist circumference, waist-to-height ratio (WHtR) and BMI. Previously, different testing positions and methods were performed. Hence, this study aims to examine the relationship between anthropometric measurements and isokinetic trunk strength measured in the sitting position and in an athletic population.
Methods: Age, sex, weight, height, waist circumference, BMI and WHtR obtained from 1480 participants were analyzed regarding their relationship to parameters of isokinetic trunk strength (torque, power and work). Statistics were performed by Pearson-correlation and mixed linear models.
Results: Greater weight, height, waist circumference, BMI, WHtR and male sex were related with greater isokinetic trunk strength. Increasing age was associated with lower isokinetic trunk strength. There is no relevant relation between anthropometric variables and flexion-/extension-ratios. Factors related to isokinetic trunk strength can be ordered in the following ranking: BMI>age>WHtR.
Discussion: Relations of anthropometric factors with isokinetic trunk extension and flexion strength measured in the sitting position are comparable to trunk strength measured with other measurement techniques. Modern anthropometric measurements and indices like waist circumference and WHtR are related with trunk strength as well.
Conclusions: Professionals using isokinetic measurements should be aware of the association with anthropometric factors.
Key words: Core Strength, Age, Waist Circumference, Body-Mass-Index (BMI), Waist-to-Height-Ratio (WtHR)
Zusammenfasssung
Problemstellung: Zusammenhänge zwischen anthropometrischen Größen und isokinetischer Rumpfkraft sind für Alter, Geschlecht, Gewicht und Größe in einer gesunden Bevölkerung sowie für den Body-Mass-Index (BMI) in einer fettleibigen Bevölkerung bekannt. Für den Taillenumfang, die Waist-toHeight-Ratio (WHtR) und den BMI liegen kaum Daten vor. Da in früheren Studien unterschiedliche Testpositionen und -methoden verwendet wurden, zielt diese Studie darauf ab, den Zusammenhang zwischen anthropometrischen Größen und im Sitzen gemessener isokinetischer Rumpfkraft in einer sportlich ambitionierten Population zu untersuchen.
Methoden: Alter, Geschlecht, Gewicht, Größe, Taillenumfang, BMI und WHtR von 1480 Probanden wurden auf ihren Zusammenhang mit Parametern der isokinetischen Rumpfkraft (Drehmoment, Leistung und Arbeit) untersucht. Die Statistik wurde mittels Pearson-Korrelation und gemischter linearer Modelle durchgeführt.
Ergebnisse: Ein höheres Gewicht, eine höhere Körpergröße, ein höherer Taillenumfang, ein höherer BMI, eine höhere WHtR und das männliche Geschlecht waren mit einer höheren isokinetischen Rumpfkraft verknüpft. Zunehmendes Alter hing mit einer geringeren isokinetischen Rumpfkraft zusammen. Es gibt keinen relevanten Zusammenhang zwischen anthropometrischen Variablen und Flexions-/Extensionsverhältnissen. Hinsichtlich der Stärke des Zusammenhanges mit der isokinetischen Rumpfkraft konnte eine Rangfolge ermittelt werden: BMI>Alter>WHtR.
Diskussion: Die Wechselwirkungen anthropometrischer Faktoren mit der im Sitzen gemessenen isokinetischen Rumpfstreckund -beugekraft sind vergleichbar mit der mit anderen Messverfahren gemessenen Rumpfkraft. Moderne anthropometrische Maße wie der Taillenumfang hängen in vergleichbarer Weise mit der Rumpfkraft zusammen.
Schlussfolgerungen: Sportmediziner, die isokinetische Messungen durchführen, sollten sich der Wechselwirkungen mit anthropometrischen Faktoren bewusst sein.
Schlüsselwörter: Rumpfkraft, Alter, Taillenumfang, Body-Mass-Index (BMI), Taille-zu-Größe-Verhältnis (WtHR)
Introduction
The measurement of isokinetic trunk strength is a safe and accepted method for quantifying trunk strength not only in sports medicine, but also in the treatment and rehabilitation of back pain (14, 15, 17, 19, 24, 34, 41, 43). Advice on trunk strength training is a key element of professional intervention, particularly in sports and rehabilitation medicine. High trunk strength can lead to advantages in performance, in example as a predictor of pedalling power in elite racing cyclists (30), or in the prevention of injuries, in example in reducing non-contact lower extremity sprain and or strain in soccer players (1). In patients with extremity impairment, it is not possible to measure trunk strength in the standing position or using field tests, like the double-leg-lowering test or Biering-Sorensen-test (13, 40). Therefore, isokinetic measurement in the sitting position is a reliable method for assessing trunk strength (19, 33). Furthermore, anthropometric measurements during the intervention and observation of athletes or patients in training and rehabilitation are necessary to provide professional advice based on changes in the body composition. Finally, relations between trunk strength and anthropometric changes during the intervention are feasible.
Extensive data exist on the relationship between anthropometric factors and isokinetic trunk strength measured in the standing position. Associations were found between age (8, 17, 20, 35, 39), sex (2, 10, 18, 27), height (11, 17), and weight (2, 8, 10). In obesity research, body mass index (BMI) and waist-to-height ratio (WHtR) have been identified as influencing factors (3, 16, 21, 29. A higher waist circumference, which indicates abdominal obesity, was estimated to lead to a higher flexion peak torque in equation models for trunk strength (31). Since most of the previous studies are more than 20 years old, it is unknown whether those previous results can be still applied to modern isokinetic devices.
Isokinetic trunk strength measurements in the standing and sitting positions can differ for several reasons. Possible influencing factors include different testing setups, gravity compensation, pre-tension of the muscles, participation of the hip flexors and extensors in trunk extension and flexion, starting position in the hip joint and the specified range of motion (7, 13, 38, 43). Therefore, the data acquired in the standing position must be confirmed.
Previously, only three studies have measured isokinetic trunk strength in a sitting position (9, 21, 25). Although the relationships between age, sex, height, BMI, and the isokinetic trunk strength in the sitting position are known (9/a>, 21, 26), no relationship has yet been reported between waist circumference and the WHtR. These anthropometric factors are a central tool not only for the prediction of abdominal obesity and cardiovascular health but also in sports and rehabilitation medicine because professionals provide diet or training advices depending on pathological or non-pathological values (23). Furthermore, most isokinetic studies focussed on trunk extension. Trunk flexion matters when throwing overhead or when canoeing is the main discipline, and hence it should be considered (42, 43).
There is a well known relationship between anthropometric measurements and trunk strength in the standing position. Modern tests are performed in a sitting position and measures can differ due to the changed range of movement (ROM) in the hip during measurement (13). Therefore, it is necessary to evaluate different measures and associations in athletic populations in the sitting position. It is necessary to demonstrate this in an athletic population, as isokinetic measurements are frequently performed on athletes. To date, torque, work, and power parameters have been considered separately. A complete dataset should be provided here.
Materials and Methods
Experimental Approach to the Problem
This study was a retrospective analysis of participants tested between 2008 and 2018. Anthropometric measurements of the following metric variables were performed (as the independent variables): age, sex, height, body weight, and waist circumference. BMI and WHtR were also calculated. Before starting the isokinetic assessment, the participants had a personal appointment with an orthopedic surgeon for the collection of medical history and examination. The exclusion criteria for isokinetic measurement were acute illness, acute pain, or structural damage to the spine (acute disc herniation, spinal implants, tumours, and fractures) which would lead to incorrect data. For the best reliability of isokinetic measurements, instructions from previous studies were considered (2,17, 18, 25, 32, 35). The following metric isokinetic measurement parameters were the dependent variables representing flexion and extension trunk strength: absolute and average parameters of torque, work, power, and total work as well as the flexion-to-extension ratios of all parameters. Data were collected retrospectively from the archive and digitally from the isokinetic device in MS Excel format and transformed into SPSS-Data.
Subjects
A total of 1,480 participants (1,372 male and 108 female soldiers) who underwent routine checkups were included in this study. Isokinetic and anthropometric measurements were performed once or several times between 2008 and 2018. Out of the 1480 participants, 732 were assessed only once, 231 twice, 134 three times, 83 four times, 108 five times, 103 six times, 62 seven times, 20 eight times, two nine times, two ten times, one eleven times, one 12 times and one 13 times. Depending on the analyzed parameters, 3,172-3,754 samples were obtained. All anthropometric measurements (age, height and weight, and waist circumference) were recorded by medical assistance personnel on the day of the isokinetic measurements. Waist circumference measurements were made in a horizontal line halfway between the crista iliaca and the inferior costal arch, according to WHO recommendations (44). BMI was calculated as: weight (kg) / (height (m))². WtHR was calculated as waist circumference (m) / height (m) The results of the anthropometric measurements are shown in table 1.
All of the participants provided written consent to the use of their data for research before measurement. The local and institutional ethics boards approved this study (file number: A2019-0123), which was conducted following the Declaration of Helsinki.
Procedures
The isokinetic device IsoMed2000 (D.&R. Ferstl, Hemau, Germany) was used to assess trunk strength. This device includes gravitational compensation (2, 17, 25, 35). As recommended in earlier studies, the participants were seated on an isokinetic device after a ten-minute warm-up on a bicycle-ergometer, and the measurements were acquired under the supervision of an experienced examiner who encouraged the participant to exert maximum effort (18, 25, 32). The procedure consisted of 10 repetitions at an angular velocity of 90 degrees per second (17, 35). The range of motion was -24 to +22°, starting from 90° flexion of the hip joint. All the parameters were measured separately for trunk extension and flexion. The following measured values were referred to as absolute parameters: peak torque (Newtonmeter, Nm), peak work (Joule, J), peak power (Watt, W) and total work (Joule, J). The peak parameters were the best out of 10 repetitions, and the total work was summed up from 10 repetitions. The average parameters denoted the average values from 10 repetitions of the peak torque, peak work, and peak power. The flexion-to-extension ratios of the absolute and average parameters were calculated. Isokinetic measurements were performed at least one month apart to avoid intra-individual learning effects. There was no control group or condition, however, 24 subjects were examined twice in within 0-2 days. Coefficients of variation and intraclass correlations-(ICCs) were calculated from that data. ICCs were calculated one-way random and thus corresponded to Type (1,k) according to Shrout & Fleiss (36) or Type K as per McGraw & Wong (22).
Statistical Analysis
The export function of the IsoMed 2000 device was used to output data as comma separated values (CSV) files. These files were digitally transformed using Excel-based-software and checked for plausibility. SPSS Version 23 (IBM, Armonk, NY, USA) was used for the statistical analysis. Data were first transformed into a long-range format in order to consider repeated measurements. Normal distribution was analyzed visually owing to the known limitation of Kolmogorov-Smirnov and Shapiro-Wilk tests in large sample sizes (12). A normal distribution was demonstrated for the measured variables of height, weight, BMI, and WHtR. No normal distribution was demonstrated for age and sex as the population of soldiers mainly consisted of young and male participants (age range 18-81 years, percentage of male participants 95,74%). Subsequent statistical procedures were performed under the assumption of the central limit theorem. Using further descriptive statistics, the metric variables were analyzed using Pearson’s product-moment correlation to calculate the Pearson correlation coefficient (r). Cohen´s rules were used to interpret the strength of correlation (6). Regression analyses were performed separately for each isokinetic parameter to quantify the correlation between the anthropometric variables and dependent isokinetic parameters. Mixed linear regression models were used to consider the intraindividual effects of up to 13 measurements per participant over the observation period. Subsequently, the residuals, and thus the error terms, were visually checked for normal distribution using a histogram and Q-Q-plot. Due to multicollinearity, not all anthropometric influencing variables were included in the regression analyses. Only age, BMI and WHtR were included in the analyses to produce comparable models. Sex as a dichotomic variable was not included in regression analyses, because the predominantly male study population was not applicable to investigate differences between the sexes. Owing to the large numerical differences in the regression coefficients (RCs), the T-statistic was used. In regression analyses, the T-statistic allowed for more comparable results. The T-statistic was calculated by dividing the RC by the standard error. With zero variance, one result was confirmed by a generalized linear model, which was checked for heteroscedasticity using the Breusch-Pagan test and the residuals were visually checked for normal distribution. No differences were observed in the RCs of the mixed linear model. Significance was reached when p ≤ 0.05. All isokinetic parameters provided good reliability (coefficients of variation<0.19, and ICC>0.82, except for the average torque of trunk flexion=0.656).
Results
Isokinetic Measurements
Table 2 shows the results of the isokinetic measurements.
Relation to Sex and Age
Female sex and increasing age correlated with decreasing absolute and average parameters of torque, work, power, and total work (table 3). While a moderate to strong correlation was observed for sex, a weak correlation was observed for age (table 3). In the regression analyses, older age was negatively associated with absolute and average parameters of torque, work, power, and for the total work (table 6). A greater quantitative decrease in extension than in flexion can be determined per year of life. For example, peak torque extension decreased by 2.9 Nm per year of life, and peak torque flexion by 1.1 Nm per year of life. The highest age-related absolute decrease was observed in total work at extension. The strongest decrease, corrected for the standard error, was observed in the peak torque for trunk extension. Flexion-to-extension ratios correlated very weakly with age and sex (table 4). The correlations between age and flexion-to-extension ratios could not be quantified using mixed linear models due to missing normal distribution of the residuals.
Relation to Height and Weight
Higher height and weight were correlated with increased isokinetic trunk strength in the absolute and average parameters of torque, work, power and total work (table 3). Body weight showed a strong correlation, while height showed a moderate to strong correlation (table 3). Higher weight was weakly correlated with lower flexion-to-extension ratios (table 4), and no significant correlation was observed for height (data not shown). However, the effects of height and weight could not be quantified using the mixed linear models. The correlations between height respectively weight and flexion-to-extension ratios could not be quantified using mixed linear models due to missing normal distribution of the residuals.
Relation to Waist Circumference
A larger waist circumference was weakly correlated with higher absolute and average values of torque, work, power and total work (table 3), whereas no significant association with the flexion-to-extension ratios could be detected (data not shown). It was not possible to quantitatively analyze the correlations of the waist circumference in the mixed linear models. The correlations between waist circumference and flexion-to-extension ratios could not be quantified using mixed linear models due to missing normal distribution of the residuals.
Relation to BMI and WHtR
Higher BMI was moderately correlated with increasing absolute and average values of torque, power, work, and total work (table 5). In the regression analyses, this was confirmed by a high level of significance for all absolute and average parameters of torque, power, work, and total work (table 6). A higher BMI correlated very weakly with lower flexion/extension ratios. (table 4). The association between BMI and the flexion/extension ratios could not be quantified using mixed linear models due to missing normal distribution of the residuals. A higher WHtR was weakly correlated with higher absolute and average values of isokinetic trunk strength (table 5). In the regression models, strong negative and positive RCs were detected in some cases (table 6). The correlations between WHtR and flexion-to-extension ratios could not be quantified using mixed linear models due to missing normal distribution of the residuals.
Ranking of the Influencing Factors
One of the goals was to use regression analyses to rank the relationship between anthropometric variables and trunk strength. Owing to the lack of normal distribution of the residuals in the regression analyses for the flexion-to-extension ratios and multicollinearity in the models, including independent variables such as sex, height, weight and waist circumference, only three factors could be listed in this ranking. According to the RCs alone, the strength of the correlation of the three anthropometric variables with the absolute and average parameters of isokinetic trunk strength can be ordered as follows: WHtR (average RC=-3540,273-158,086 [the strongest factor in 14/14 models])>BMI (average RC=4,841-102,179)>age (average RC=-20,860 to-11,736). According to the T-statistics and level of significance (p-value), the ranking of the three anthropometric variables changed in the following manner: BMI (average T-statistics=27,963-22,979 [the strongest factor in 13/14 models]; average p-value=1,1917*e-90-3,6674 *e-31 [the strongest factor in 14/14 models])>age (T-statistics=-20,860 to -11,736 ; average p-value=5,6714*e-154-3,3411*e-108)>WHtR (T-statistics=-15,844-10,279 ;average p-value=1,8146*e-54-2,1455*e-24). Notably, the t-statistics were more comparable. Accordingly, we preferred the following ranking: BMI>Age>WtHR.
Discussion
Concordant with previous research, significant positive relationships of height, weight, and male sex, as well as negative relationships of female sex and age, on the isokinetic trunk strength could also be shown for isokinetic trunk strength measured in the sitting position (2, 8, 9, 10, 11, 17, 20, 27, 32, 35). Despite the different test conditions, evidence from research with different testing positions and different measurement approaches showed comparable results (2, 8, 10, 17, 27, 32, 39). Garcia-Vacquero et al. postulated the need for further investigations into the association between anthropometric parameters and trunk strength (14). The results of the present study describe the relationship of all common anthropometric factors concerning trunk strength.
BMI and WHtR had a positive relationship with isokinetic trunk strength. With an increase in anthropometric parameters (BMI, WHtR, weight, and waist circumference) indicating low cardiovascular fitness and high cardiovascular risk, trunk strength also increased. Previous studies have also described this paradox. Most of these studies have described a positive correlation among body weight, BMI, and absolute trunk strength (3, 5, 16, 28, 31, 37).
The results of this study suggest, that waist circumference is a relevant influencing factor in the seated measuring position, too (28). Higher waist circumference values correlated with a higher extent of trunk strength, and the correlation coefficients were slightly higher for the trunk flexion parameters. In this athletic population, a higher waist circumference probably indicated greater muscle mass in the flexors and extensors. Whether the relationship with the trunk extensors is more important than that with the flexors in an obese population is unknown. However, it is plausible, as with increasing waist circumference, indicating abdominal obesity, that the center of mass is shifting to the anterior inferior and hence more leverage of mainly the trunk extensors is needed to maintain an upright body position (31).
The relation between anthropometric measurements and the flexion-to extension ratios was either very weak or missing and was probably not relevant.
While absolute parameters represent the best out of 10 repetitions and show maximal trunk strength, average parameters, especially the total work, express trunk strength endurance. Anthropometric parameters are also related to isokinetic trunk strength parameters.
As trunk flexion parameters are also related to anthropometric variables, not only the known linear increase in the muscle mass and thickness of the erector spinae but also an increase in ventral trunk muscle mass and total muscle mass results in higher isokinetic strength and endurance (7, 18, 35). Finally, this assumption is plausible as the trunk muscles need more leverage to maintain trunk position with increasing weight and height, which results in higher isokinetic trunk strength (31, 37). The analyzed population consisted predominantly of young soldiers. Female and older participants were also underrepresented. However, the absolute number of female participants was comparable to that in previous studies (3, 9, 16, 18, 26). Despite the low percentage of female participants, there was a significant relationship between sex and trunk strength in the regression models.
Only Timm et al. reported a comparable number of participants of both sexes (39). In that study, trunk strength testing was performed in the standing position without gravity compensation (exclusively for trunk extension). They demonstrated the relationship between trunk extension, sex, and age.
Other studies reported comparable relationships between anthropometric factors and trunk strength. In most of these studies, trunk strength measurements differed and icluded maximum bearable weight lifting (37), isometric measurements of trunk strength (28), and isokinetic trunk strength in a standing position (2, 3, 11, 16, 20, 35, 39).
In the holistic approach of this study, the relationships of several anthropometric variables with all relevant parameters of isokinetic trunk strength, expressed in the physical quantities of torque, work, and power, which were measured in the sitting position, could be analyzed. Previously, only three studies were performed using comparable measurement techniques in a sitting position, but with smaller study populations (9, 21, 26). Isokinetic trunk strength measurements in standing and sitting positions can lead to different results (7, 13, 38, 43). It is worth mentioning, that we showed the quantitative effects of anthropometric changes on all isokinetic parameters of trunk strength. For example, with a one-year age increase, the peak torque decreased by 1,024 Nm in trunk flexion and 3,341 Nm in trunk extension (Table 6). An increase of one BMI point resulted in an increase of 9,972 Nm in trunk flexion and 21,991 Nm in trunk extension. An increase of 0,01 in WHtR resulted in a 3,125 Nm increase in trunk flexion and 6,843 Nm in trunk extension. With these benchmarks, professionals can better understand and interpret the trunk strength changes in athletes due to anthropometric alterations. Although Pajoutan et al. showed a difference in relative isometric trunk strength in a small population of participants with obesity, further research is necessary for obese and non-obese populations regarding the association of pathological values of BMI and WHtR with isokinetic trunk strength (4, 28).
There are many limitations to the statistical analysis. Only age, BMI, and WHtR were included in mixed linear models. No alternative mixed linear or generalized linear model that met the quality criteria and included more anthropometric variables were created. Although a low numerical variation in WHtR (0.49±0.06) and a larger numerical variation in BMI (26.1±3.1) and age (37.9±10.2 years) were associated with similar changes in trunk strength, the RCs were not comparable. For this reason, the level of significance (p-value) and T-statistics were used to better distinguish the strength of the relationship. The study population mainly consisted of male athletic soldiers.
Consequently, no conclusions could be drawn regarding different populations. Other results are feasible in obese populations. Furthermore, using correlation and regression analyses, it was not possible to conclude the cause and effect. Mixed linear regression was used to reduce intra-individual effects with up to 13 repeated measurements, however, intra-individual effects were still feasible. This is necessary because with the trunk, in contrast to the measurement of the strength at the extremities, there is no opposite side for the intra-individual comparison. At first glance, the younger (37,9±10,2 years, age range 18-81) and more athletic population may be a limitation, but on the other hand it is an advantage, as it creates a dataset for this specific population of male and active subjects that can help to guide training advice for almost all age groups of patients in sports and rehabilitation medicine.
To the authors knowledge, this was the first study to establish a ranking of the relationship between anthropometric parameters and isokinetic trunk strength after considering the entire spectrum of isokinetic parameters.
Conclusion
Trunk strength is a key element in the success of interventions, particularly in rehabilitation and sports medicine. In patients with pain or injuries to the extremities, trunk strength should not be measured in the standing position or during field tests. The results of this study suggest that there seems to be no difference in the relationship of isokinetic trunk strength with anthropometric parameters when compared with the standing position in an athletic population. For current anthropometric parameters such as waist circumference, BMI, and WHtR, a relationship with trunk strength was observed. Concerning the absolute and average parameters of torque, work, power, and total work, a ranking of importance was created to describe the amount of influence for three of them: BMI>Age>WHtR.
Overlapping with obesity research, there is a positive relationship between trunk extension and flexion strength and body weight, height, waist circumference, BMI, and WHtR in an athletic population.
During observation of athletes and patients in rehabilitation medicine, several anthropometric and trunk strength measurements are performed. Professionals should be aware of the interactions between anthropometric factors and trunk strength and should improve their advices for patients during training and rehabilitation.
Conflict of Interest
The authors have no conflict of interest.
Literatur
- A comparative study of core musculature endurance and strength between soccer players with and without lower extremity sprain and strain injury. Int J Sports Phys Ther. 2019; 14: 525-536.
- Trunk muscle strength in athletes. Med Sci Sports Exerc. 1988; 20: 587-593.
- Isokinetic Measurement of Trunk Muscle Strength in Women with Chronic Low-Back Pain. Am J Phys Med Rehabil. 2001; 80: 650-655.
- Comparison of isokinetic trunk flexion and extension torques and powers between athletes and nonathletes. J Exerc Rehabil. 2018; 14: 72-77.
- Reliability analyses and values of isometric shoulder flexion and trunk extension strengths stratified by body mass index. PLoS One. 2019; 14: e0219090.
- Statistical power analysis for the behavioral sciences.Academic press, 2013.
- Influence de la position de test sur l‘évaluation isocinétique lombaire [Influence of testing position on lumbar isokinetic measurements]. Ann Readapt Med Phys. 2002; 45: 12-18.
- Age, weight, and the front abdominal power test as predictors of isokinetic trunk strength and work in young men and women. J Strength Cond Res. 2009; 23: 915-925.
- Isokinetic and isometric muscle strength in a healthy population with special reference to age and gender. Acta Physiol (Oxf). 2009; 197: 1-68.
- Peak torque-to-body weight ratios in the trunk: a critical analysis. Phys Ther. 1989; 69: 138-143.
- Anthropometric variables, self-efficacy beliefs, and pain and disability ratings on the isokinetic performance of low back pain patients. Spine. 1994; 19: 941-947.
- Discovering Statistics Using IBM SPSS Statistics, 5th Edition. 5th ed. SAGE Publication ltd., 2017. https://uk.sagepub.com/en-gb/eur/discovering-statistics-using-ibm-spss-statistics/book257672 [8 April 2023].
- Sitting vs. Standing Isokinetic Trunk Extension and Flexion Performance Differences. J Strength Cond Res. 2000; 14: 310-315.
- Isokinetic trunk flexion–extension protocol to assess trunk muscle strength and endurance: Reliability, learning effect, and sex differences. J Sport Health Sci. 2020; 9: 692-701.
- Training the Trunk for Improved Athletic Performance. Strength Condit J. 2000; 22: 50.
- Assessment of Isokinetic Muscle Strength in Women Who Are Obese. J Orthop Sports Phys Ther. 2002; 32: 347-356.
- Isokinetic performance capacity of trunk muscles. Part I: The effect of repetition on measurement of isokinetic performance capacity of trunk muscles among healthy controls and two different groups of low-back pain patients. Scand J Rehabil Med. 1996; 28: 201-206.
- Comparison of trunk strength measurements between two different isokinetic devices used at clinical settings. J Spinal Disord. 1997; 10: 391-397.
- Usefulness of measuring isokinetic torque and balance ability for exercise rehabilitation. J Exerc Rehabil. 2015; 11: 65-66.
- Predictors of isokinetic back muscle strength in patients with low back pain. Spine. 1999; 24: 275-280.
- The Relationship between Cross Sectional Area and Strength of Back Muscles in Patients with Chronic Low Back Pain. Ann Rehabil Med. 2012; 36: 173-181.
- Forming inferences about some intraclass correlation coefficients. Psychol Methods. 1996; 1: 30-46.
- Selection of anthropometric indicators for classification of abdominal fatness— a critical review. Int J Obes. 1998; 22: 719-727.
- The Relationship Between Core Stability and Performance in Division I Football Players. J Strength Cond Res. 2008; 22: 1750-1754.
- Trunk strength testing with iso-machines. Part 1: Review of a decade of scientific evidence. Spine. 1993; 18: 801-811.
- Normal Trunk Muscle Strength and Endurance in Women and the Effect of Exercises and Electrical Stimulation: Part 1: Normal Endurance and Trunk Muscle Strength in 101 Women. Spine. 1987; 12: 105-111.
- The relationship of disability (Oswestry) and pain drawings to functional testing. Eur Spine J Off Publ Eur Spine Soc Eur Spinal Deform Soc Eur Sect Cerv Spine Res Soc. 2000; 9: 208-212.
- Obesity effect on isometric strength of the trunk extensors. Proc Hum Factors Ergon Soc Annu Meet. 2016; 60: 943-947.
- The Study on Relation of Obesity and Low Back Pain Based on Body Composition Using Segmental Bioelectrical Impedance Analysis and Isokinetic Trunk Muscle Strength. J Korean Med Rehabil. 2009; 19: 289-302.
- Comparison of maximum muscle strength and isokinetic knee and core muscle functions according to pedaling power difference of racing cyclist candidates. J Exerc Rehabil. 2019; 15: 401-406.
- Body segment inertial parameters and low back load in individuals with central adiposity. J Biomech. 2014; 47: 3080-3086.
- Isokinetic trunk-strength deficits in people with and without low-back pain: a comparative study with consideration of effort. J Spinal Disord. 1991; 4: 68-72.
- Absolute and relative reliability of isokinetic and isometric trunk strength testing using the IsoMed-2000 dynamometer. Phys Ther Sport. 2017; 24: 26-31.
- Core-Muscle Training and Neuromuscular Control of the Lower Limb and Trunk. J Athl Train. 2019; 54: 959-969.
- Die isokinetische Kraftleistungsfähigkeit der Rumpfmuskulatur von Patienten mit chronischen Rückenschmerzen [Isokinetic strength of lumbar muscles in patients with chronic backache]. Z Orthop Unfall. 1997; 135: 315-322.
- Intraclass correlations: Uses in assessing rater reliability. Psychol Bull. 1979; 86: 420-428.
- Obesity does not reduce maximum acceptable weights of lift. Appl Ergon. 2009; 40: 1-7.
- Choosing the Right Body Position for Assessing Trunk Flexors and Extensors Torque Output. Hum Mov. 2011; 12: 57-64.
- Isokinetic lifting simulation: a normative data study. J Orthop Sports Phys Ther. 1988; 10: 156-166.
- Tests to Measure Core Stability in Laboratory and Field Settings: Reliability and Correlation Analyses. J Appl Biomech. 2019; 35: 223-231. doi:10.1123/jab.2018-0407
- Core Stability and Its Relationship to Lower Extremity Function and Injury. J Am Acad Orthop Surg. 2005; 13: 316-325.
- Effects of Isokinetic Training on Trunk Muscle Fitness and Body Composition in World-Class Canoe Sprinters. Front Physiol. 2019; 10: 21.
- Isokinetic trunk strength, validity, reliability, normative data and relation to physical performance and low back pain: A Review of the Literature. Int J Sports Phys Ther. 2020; 15: 160-174.
- Waist circumference and waist-hip ratio: report of a WHO expert consultation. 2008. https://www.who.int/publications-detailredirect/9789241501491 [13 September 2023]
Effects of Caffeine-Containing Energy Drinks on Endurance Performance and Side Effects: A Randomized Cross-Over Study
Auswirkungen von koffeinhaltigen Energydrinks auf Ausdauerleistung und Nebenwirkungen: Eine randomisierte Cross-Over-Studie
Summary
Introduction: After caffeine consumption of 3-6 mg/kg, significant increases in endurance performance have been observed in studies, with various side effects occurring. The aim of this study is to analyse whether caffeine intake of 2 mg/kg increases endurance performance while avoiding side effects.
Methods: In two sessions, 13 women and 19 men between 20 and 30 years (24.5±1.9 years) took 2mg caffeine/kg in the form of an energy drink or a placebo. After 60 minutes, participants started with an incremental test on a treadmill to exhaustion. Heart rate and oxygen uptake were measured and immediately afterwards they indicated received perceived exertion (RPE). The morning after, the subjects fill out a questionnaire with 24 items (GBB-24) to analyse their health and symptoms. Before the investigation was carried out, the responsible members of the institutional ethics committee reviewed the study protocol.
Results: In comparison to placebo drink, the ingestion of energy drink with 2 mg caffeine/kg increased running time (7:23±1:03 vs. 7:16±1:03 min; p<0.05) and VO˙ 2 max (47.24±6.5 vs. 45.72±6.2 ml O2 /min/kg; p≤0.05). The heart rates during running as well as the RPE and answering the questionnaire items did not provide any statistical differences between energy drink and placebo group.
Conclusion: Thus the ingestion of the energy drink with a dose of 2mg of caffeine/kg did not affect the prevalence of negative side effects but might be an effective ergogenic aid to improve endurance performance.
Key words: Endurance Exercise, Incremental Test, Sports Nutrition, Beverages
Zusammenfassung
Einleitung: Nach Koffeinkonsum von 3-6 mg/kg wurden in Studien signifikante Steigerungen der Ausdauerleistung beobachtet, wobei häufig verschiedene Nebenwirkungen auftraten. Ziel dieser Studie ist es zu analysieren, ob ein Koffeinkonsum von 2 mg/kg die Ausdauerleistung steigert und gleichzeitig Nebenwirkungen vermeidet.
Methoden: In zwei verschiedenen Sitzungen nahmen 13 Frauen und 19 Männer im Alter zwischen 20 und 30 (24,5±1,9 Jahre) 2mg Koffein/kg in Form eines Energydrinks oder ein Placebos ein. Nach 60 Minuten starteten die Teilnehmer mit einem Stufentest auf einem Laufband bis zur Erschöpfung. Dabei wurden Herzfrequenz und Sauerstoffaufnahme gemessen und unmittelbar danach gaben die Probanden den Grad der empfundenen Anstrengung (RPE) an. Am Morgen des Folgetages füllten die Probanden einen Fragebogen mit 24 Items (GBB-24) aus, um das Gesundheitsempfinden und die Beschwerden zu analysieren.
Ergebnisse: Im Vergleich zum Placebo-Getränk verlängerte die Einnahme von Energy-Drinks mit 2 mg Koffein/kg die Laufzeit (7:23±1:03 vs. 7:16±1:03 min; p<0,05) und die VO˙ 2 max (47,24±6,5 vs 45,72±6,2 ml O2 /min/kg, p≤0,05). Die Herzfrequenzen beim Laufen sowie der RPE und die Beantwortung der Fragebogen-Items ergaben keine statistischen Unterschiede zwischen Energy-Drink- und Placebo-Gruppe.
Schlussfolgerung: Somit hatte die Einnahme des Energy Drinks mit einer Dosis von 2mg Koffein/kg keinen Einfluss auf die Prävalenz negativer Nebenwirkungen, konnte aber ein wirksames ergogenes Hilfsmittel zur Verbesserung der Ausdauerleistung sein.
Schlüsselwörter: Ausdauerbelastung, Stufentest, Sporternährung, Sportgetränke
Introduction
In the first years on the market energy drinks became known as “ ‘speed in a can’, ‘liquid cocaine’ and a ‘legal drug’ ” (15). They are advertised as fashion drinks for energy increasing, avoiding fatigue and improving mental awareness (4, 11). On the other hand, the effects are associated with insomnia, nervousness, headache, rapid heartbeat and increased blood pressure (1).
In addition to the health-damaging effects of energy drinks, they are also known for their energy-providing effects. Doherty and Smith analysed studies on caffeine consumption for endurance performance in their meta-analysis. In these studies caffeine doses were taken between 3-13 mg/kg body weight. Compared to meta-analyses also showed significant increases in endurance performance after caffeine consumption of 3-6 mg/kg (17, 18). In addition, it was observed that caffeine consumption of more than 3 mg/kg could include side effects like tachycardia, nervousness, activeness, insomnia, headache and gastrointestinal problems (5, 6, 14).
Due to the performance-enhancing effects of caffeine at 3-6 mg/kg body weight as an ingredient in energy drinks, in particular on endurance performance and the reported side effects, the effects of lower dosages should be investigated (8). Therefore, this study investigated whether ingestion of 2 mg/ kg caffeine one hour before exercise in an ergometer incremental test increased endurance performance in comparison to a placebo drink. Furthermore, it should be shown whether and which kind of side effects are associated with the intake of the energy drink.
Methods
The current study was conducted in accordance to the Helsinki declaration guidelines. Before the investigation was carried out, the responsible members of the institutional ethics committee reviewed the study protocol. Participation was voluntary and all participants consented to participation by signing an informed consent form prior to participation. Totally 35 participants between 20 and 30 years volunteered to take part in this study. The results of three participants were excluded of this study because of missing criteria of complete exhaustion, too low run-time or caffeine-intake before the testing so that thirty-two databases (19 male, 13 female) are included in the analysis. Subjects had a mean±SD age of 24.5±1.9 years, height of 179.0±10.1 cm and body mass of 74.2±11.8 kg before placebo energy drink ingestion and 74.0±12.1 kg before energy drink ingestion. Before each testing the participants were asked to fill out anamnesis questionnaires. Following these anamnesis of each participant they did not receive medical treatment, had neither acute or chronical diseases and were sporty fully resilient. All participants were asked to refrain from vigorous exercise, do not consume caffeine 24 hours before testing and to have a light meal two hours before the test. Participants were informed of any risks associated with the experiments before giving their written consent to participate. The study was carried out in accordance with the Declaration of Helsinki.
A placebo-controlled and randomized crossover design was used. Each participant performed two different experimental trials under the same conditions. On one occasion, participants ingested an amount of fluid of a commercially available, caffeine-containing energy drink (ROCKSTAR©) with 2 mg caffeine/kg body mass (2 mg/kg), 750 mg sugar/ kg body mass and other ingredients. On other occasion, participants ingested the same amount of fluid with the same sugar content but without caffeine and the other ingredients (placebo; 0 mg/kg). The experimental trials were separated by at least of 48 hours to allow complete caffeine washout. The drinks were distributed double-blind after the participants had previously been randomized, so that 18 subjects received the energy drink and 14 subjects received the placebo drink at the first time of the test.
Thus, subjects started an incremental test on the treadmill (pulsarTM, h/p/cosmos, Germany) 60 minutes after consuming the energy drink. The subjects should run on the treadmill as long as they were able to achieve their subjective exertion. The test started at a speed of 7.2 km/h (2 m/s) and every minute the speed increased by 1.8 km/h (0.5 m/s). The incline angle of the treadmill was 1% throughout the test. Oxygen uptake and heart rate were measured by a mobile spirometry system (MetaMax 3bTM, Cortex, Germany) and the total running time was determined. Immediately after the end of the test, the subjects indicated received perception of exertion (RPE) at the last speed level. The subjects were encouraged not to consume any caffeinated foods until the next day. The next morning after testing, the subjects filled out a questionnaire with 24 items, called Giessen Subjective Complaints List (GBB-24) (3).
Differences of total running time, V˙O2 max and heart rates were analysed by paired t tests.
The prerequisites of the normal distribution by using the Shapiro-Wilk test for carrying out the tests were fulfilled. Difference in RPE and items of the questionnaire GBB-24 were analysed using the Wilcoxon signed-rank test. Data were analysed with the statistical package SPSS V25 (SPSS Inc., Chicago, IL, USA). The significance level was set at p ≤ 0.05.
Results
In comparison to the placebo, the pre-exercise ingestion of the caffeinated energy drink significantly increased total running time (7:23±1:03 vs. 7:16±1:03 min; p < 0.05; d=0.38) and V˙O2 max (47.24±6.5 vs. 45.72±6.2 ml O2 /min/kg; p ≤ 0.05; d=0.41). According to the latter, oxygen uptake data from six participants had to be excluded from the analyses due technical Problems.
In addition, in both groups the RPE after exhaustion had an average of 18 (p=0.12). The heart rates during the investigation were unaffected by the caffeine ingestion at all velocity levels, for 7.2 km/h (140±14 vs. 139±16 bpm; p=0.652), 9.0 km/h (152±12 vs. 151±13 bpm; p=0.808), 10.8 km/h (163±12 vs. 162±12 bpm; p=0.434), 12.6 km/h (172±11 vs. 171±11 bpm; p=0.507), 14.4 km/h (179±10 vs. 178±9 bpm; p=0.223), 16.2 km/h (182±8 vs. 183±6 bpm; p=0.969), 18.0 km/h (185±8 vs. 185±7 bpm; p=0.645), 19.8 km/h (184±6 vs. 184±6 bpm; p=0.5) and HRmax (188±7 vs. 188±6 bpm; p=0.846). The items of the questionnaire were also unaffected by caffeine ingestion, with p-values ranging from p=0.059 to p=1.0.
Discussion
The aim of the present investigation was to determinate the effects of a low amount of caffeine ingestion on performance as well as psycho-physiological side effects. The results showed that subjects increased their running time during the incremental test on average for 7.75 seconds or a total of 4:08 minutes when the consumed 2mg caffeine per kg body weight prior to performance. The overall increase in the energy drink condition was 1.78% higher than in the placebo condition. With regard to the individual, 20 athletes stayed on the treadmill longer than the intrapersonal control group after consuming energy drinks. In comparison, the placebo group achieved better or longer times of running, only 12 times compared to the energy drink group. The mean value of the relative maximum oxygen intake from the energy drink group differed significantly from that of the placebo drink group, indicating that consuming the energy drink positively effects aerobic endurance performance (12).
The GBB-24 questionnaire was filled out in the morning after each test date to evaluate whether the consumption of a comparable low dose caffeine causes psychosomatic complaints. It revealed that no significances emerged from the comparison of the individual items after statistical analysis. However, from previous studies, items emerged that can be viewed in a focused manner, which include tachycardia, nervousness, activeness, insomnia, headache and gastrointestinal problems (5, 6, 14). Within the questionnaire used in this study, several items such as “palpitations, chasing, stumbling” (p=0.276), “feeling of pressure or fullness in the abdomen” (p=0.942), “excessive need for sleep” (p=0.490), “regurgitation” (p=0.414), “heartburn or acid regurgitation” (p=0.257), “headache” (p=0.206), “stomach pain” (p=0.317), “feeling of pressure in the head” (p=0.180 ) addressed the subjective assessment of these complaints, but none of them suggests a negative effect of the caffeine consumption.
It should be noted that a randomized placebo-controlled cross-over study was carried out in the present study. Still, there are several limitations to be mentioned that might affect the results. First, a pre-test, which precedes the first day of the test, could serve to get the subjects used to the spiroergometry on the treadmill. But due to the randomized cross-over design half of the energy drink and the placebo drink group had no prior experience with the measuring system in the first test. At the same time, the study was carried out double-blind, whereby in contrast to a blind design, an improvement in the quality of the study design was brought about, since both the test subject and the test leader did not know about the group membership and thus the drink taken on the test day.
To further ensure a high level of standardization, the subjects were informed in advance of the second day of the test about the requirements of similar nutritional and behavioural patterns, similar sporting activity, the same or similar clothing and footwear as well as about the 24-hour abstinence from caffeine before the test. The drink was consumed 60 minutes before the start of exercise and since like in many other previous studys, because the highest caffeine concentration in the blood plasma is reached within one hour after ingestion (16, 17, 18). With half-lives of one hour for taurine and four to six hours for caffeine, the amounts of caffeine or taurine taken in were rinsed out before the next day of the study (9, 16). However, we did not asked subjects to fill out a food diary to precisely record both the amount and type of food consumed to control the effect of calories or especially carbohydrate intake (14). The energy drink also contained ginseng and guarana to a very low amount (0.01%). As these plant extracts contain low amounts of caffeine, but manufacturers are not obliged to list the caffeine content of these ingredients (15), the actual amount of caffeine in the energy drinks could be slightly higher than stated on the product package.
The daily amount of caffeine ingestion could also have an influence to the results of the study. Consumption of coffee, black tea, coke or energy drinks ranged from none (n=19) to up to three or more cups a day (n=7). By qualitative inspection, these habits did not seem to affect the results, but their influence could not be analysed systematically.
Conclusions
In order to achieve a higher rate of increase in aerobic endurance, however, previous research results show that an energy drink amount of 3-6 mg caffeine/kg body weight should be consumed (8, 17, 18). Since the higher the caffeine consumption increases the probability of side effects, this recommendation should be viewed critically with a simultaneous health perspective. Examples of side effects can include nervousness, headache, restlessness, stomach problems, sleep disorders or rapid heartbeat (10, 13). In summary, it can be concluded from the study carried out that, in contrast to the placebo drink, the energy drink consumed with a caffeine content of 2 mg/kg body weight led to performance-enhancing effects of aerobic endurance and at the same time there were no negative side effects.
Conflict of Interest
The authors have no conflict of interest.
Ethical Approval
The study followed Helsinki Declaration guidelines. The ethics
committee reviewed the protocol, and participation was voluntary
with informed consent obtained from all participants.
Literatur
- An emerging adolescent health risk: Caffeinated energy drink consumption patterns among high school students. Prev Med. 2014; 62: 54-59.
- Maximal aerobic capacity on the treadmill and bicycle ergometer of boys 11-14 years of age. J Sports Med Phys Fitness. 1977; 17: 153-162.
- Der Gießener Beschwerdebogen [Giessen Subjective Complaints List] (GBB-24). Handbuch 3. Aufl, 2006. Bern: Huber
- Caffeine for Sports Performance. 2013. Champaign: Human Kinetics.
- Sports drinks and energy drinks for children and adolescents: are they appropriate? Pediatrics. 2011; 127: 1182-1189.
- Dose response effects of caffeine-containing energy drink on muscle performance: a repeated measures design. J Int Soc Sports Nutr. 2012; 9: 21.
- Effects of Caffeine ingestion on exercise testing: a meta-analysis. Int J Sport Nutr Exerc Metab. 2004; 14: 626-646.
- International society of sports nutrition position stand: caffeine and performance. J Int Soc Sports Nutr. 2010; 7: 1-15.
- Caffeine and exercise: metabolism, endurance and performance. Sports Med. 2001; 31: 785-807.
- Neuromuscular Responses to Incremental Caffeine Doses: Performance and Side Effects. Med Sci Sports Exerc. 2013; 45: 2184-2192.
- Characteristics Associated with Consumption of Sports and Energy Drinks among US Adults: National Health Interview Survey, 2010. J Acad Nutr Diet. 2013; 113: 112-119.
- Measurement of the maximum oxygen uptake Vo2max: Vo2peak is no longer acceptable. J Appl Physiol. 2017; 122: 997-1002.
- Caffeinated energy drinks - A growing problem. Drug Alcohol Depend. 2009; 99: 1-10.
- The use of energy drinks in sport: perceived ergogenicity and side effects in male and female athletes. Br J Nutr. 2014; 112: 1494-1502.
- Health Effects of Energy Drinks on Children, Adolescents, and Young Adults. Pediatrics. 2011; 127: 511-528.
- Effects of caffeine on human behaviour. Food Chem Toxicol. 2002; 40: 1243-1255.
- Establishing a relationship between the effect of caffeine and the duration of endurance athletic time trial events: A systematic review and meta-analysis. J Sci Med Sport. 2019; 22: 232-238.
- The Effect of Acute Caffeine Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis. Sports Med. 2018; 48: 1913-1928.