This is the position where the biceps brachii muscle has the lowest impact on supination strength. This resulted in a total of 8 different positions of the arm and therefore 8 tests per subject in a randomized manner. All the possible elbow and forearm positions are summarized in Table 1. Seven age groups with seven participants representing the decades of the adult population were enclosed in this study see Table 2.
The higher number of young male participants is due to the model validation and to the power analysis prior to testing. The paired -test was used for the comparison for dependent samples and the Mann—Whitney test was used for independent samples. Data was visualized with bar diagrams. Forward selection was based on tests for the regression coefficients. Independent variables with values less than 0.
The multicolinearity and anthropometric variables problem was reduced by using the Principal Component Analysis. A matrix of rotating factors was calculated with the varimax rotation with the SAS software. An original variable was determined for all rotating components with the highest factor and was included in the multiple linear regression model—dependent on the values—and was defined as the leading variable. The dominant arms of the participants were tested consecutively in the 8 possible arm positions, and then the contralateral nondominant arms were tested.
A total of 53 male participants The mean height, weight, and body mass index of the male and female participants were comparable to the average values of the German population measurements of the Federal Statistical Office [ 13 ]. The mean skinfold measurement of the dorsal and ventral upper arm of the male and female participants was higher than the average German population and measured There were no differences between the male and female participants or between the right and left side regarding the length of the upper and lower arm and the bilateral circumference of the upper arm, the wrist, and the metacarpus.
Table 3 shows a summary of the mean values of the anthropometric data. The retrieved mean supination strength and the standard deviations according to the arm positions and age are summarized in Table 4. Participants below 39 years of age showed significantly higher supination strength using the Wilcoxon test in the dominant arm compared with the nondominant arm.
This was predominantly observed in the male subgroup 8 arm positions ; the female subgroup showed a significant difference in 1 arm position. The results of the arm dominance are summarized in Table 5. The strength in the dominant arm diminishes with progressing age in both sexes. Male participants reached their maximum flexion strength, independent of the arm dominance in the 4th decade 30—39 years ; with progressing age, the flexion strength in male participants decreases.
Significance in arm dominance was visible only in the third decade with and in the eighth decade 70—80 years with. The female participants reached their maximum flexion strength in the 5th decade 40—49 years.
Arm dominance was only visible in the 5th decade with. The flexion strength of the male population was significantly higher than the female population with. The data regarding the flexion strength for both sexes is visualized in Figure 4. The forward selection of anthropometric factors showed that only the age and gender of the assessed participants were significant predictors to the supination strength of the 8 different forearm positions and arm dominance.
All other anthropometric factors did not show an effect on the supination strength. The age and gender had a significant predicting effect on the flexion strength of the dominant arm with. The upper arm length showed an additional predicting effect on the flexion strength of the nondominant arm. The other anthropometric factors did not influence the flexion strength.
This study generated gender specific reference values for the supination and flexion strength of the elbow joint for LHBT healthy adults aged 20 and above. Anthropometric factor analysis showed that only age and gender of the cohorts were significant predictors of the supination and flexion strength. Although several studies exist in testing the strength of the forearm, this study is the first to analyze the influence of the elbow angle and supination angle on the torque and to develop an age related baseline.
This baseline measurement can be used as a reference for comparison purposes in future studies. The maximum supination strength was recorded with an increasing flexion of the elbow and pronation of the forearm. In contrast, the lowest impact was registered with a maximal extension in the elbow and a pronated forearm [ 15 ]. Winters and Kleweno analyzed the strength of the upper limb with the use of a kinetic communicator Kin-Com exercise system Chattex Corp.
The fact that the greatest supination torque is achieved out of a submaximum pronation position of the forearm could be verified in several other studies as well [ 17 — 19 ]. In some study setups, the forearm of the subject lays on an adjustable armrest preventing evasive movements [ 16 , 19 ].
In our setup, the participants were instructed to keep their upper limb in the designated positions during the motion sequence allowing more natural kinesthesia. The correct motion sequence was nevertheless under the close surveillance of the examiner, positions were corrected via a goniometer, and evasive moments were prevented.
The strength tests were conducted with alternating arms and a resting pause of at least three minutes was maintained to rule out early tiring as implemented in similar setups [ 15 , 16 , 18 — 22 ]. These variables were included in our study but showed no significant influence on the supination or flexion strength of the arms. This was similar for the female population as well.
The supination values for both sexes were comparable to the results yielded in other studies with a similar setup [ 15 , 16 , 19 ]. The observation that increasing elbow flexion results in increased supination strength was also comparable to other studies [ 15 , 16 , 23 ]. This was also independent of the gender of the participants. The starting position of the forearm showed a decrease of the supination strength with increasing supination position Table 5 [ 15 — 19 , 24 , 25 ].
The generated torque during forearm rotation is dependent on the position of the pronators and supinators. The supinator and biceps brachii muscles can develop torque 4 times greater if the supination is initiated in a pronation position [ 25 ].
The flexion strength of the males was significantly higher than that of the female group. The values yielded in this study were higher than the values in other experimental setups [ 16 , 24 ]. The only difference in our setup in comparison to the others was that our participants were standing rather than sitting.
Whether the standing or sitting position affects the generated flexion torque remains unclear and requires further investigation. We observed significance in arm dominance only for the male group in the 3rd and 8th decades and for the female group in the 5th decade. This indicates that, in all other age decades, the contralateral limb can be used as a good reference by the clinician.
Shank et al. The forward selection of anthropometric variables and multiple linear regression analysis with the supination and flexion strength resulted in the development of a novel prognostic, age- and gender-dependent baseline reference. The forward selection of anthropometric variables and multiple linear regression analysis with the supination and flexion strength resulted in the development of a novel prognostic, age- and gender-dependent baseline reference with high reliability of the predictive values.
The participants were recruited in the metropolitan area of our city with additional participants from the rural areas and residents of homes for the aged. Thereby, the urban and suburban population is represented. The study was restricted to Europe typical Caucasian population. In existing publications, a greater muscle strength was described for the African population [ 15 ]. The forearms of our participants were not positioned in an adjustable armrest to prevent evasive movements during supination strength testing and the participants were standing rather than sitting.
It remains unclear whether these factors could affect the generated torque and requires further investigation. This study was designed to define reference values of supination and flexion strength of the forearm in various elbow and forearm positions as a baseline reference in a healthy population with a large sample size in an adult Caucasian population subgrouped in decades.
Furthermore, the influence of multiple anthropometric factors was investigated. The multiple linear regression analysis shows that only the age and the gender have a significant predictive impact on the supination and flexion strength. Other anthropometric factors did not have or had only a very minor influence. The data from this study could be used as a reference for comparing the healthy population to a LHBT impaired or injured population of a specific gender or age group.
This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview. Special Issues. Pietschmann , 1 Stefan Michalski, 2 Ferdinand M.
Academic Editor: Ruijin Huang. Received 15 May Revised 30 Aug Accepted 14 Sep Published 24 Oct Abstract Background. Introduction The main function of the biceps brachii muscle and its proximal tendons in the shoulder is stabilization, assistance in arm abduction, and flexion and internal rotation. Materials and Methods 2. The Participants A total of participants 55 men, mean age: Strength Measurement The isometric strength tests were performed with a custom engineered dynamometer consisting of two rotating aluminum discs interlocking at defined angles.
Figure 1. The dynamometer is connected to the computer. The vertical handle bar is intended for the supination strength whereas the horizontal one is intended for the flexion strength measurement.
Figure 2. The positions were verified with a goniometer. Table 1. Table 2. Table 3. Summary of the mean values of the various anthropometric variables of the examined male and female healthy participants. Table 4.
The mean supination strength values in newton meters Nm for the nondominant ND and dominant D limbs are matched to the 8 different arm positions. Figure 3. There was statistical significance between the elbow positions for both sexes. Table 5. Figure 4. Flexion strength in male a and female b participants in the different age groups.
Processing steps of the recorded sEMG signals after 3 kHz sampling include pre-filtering lower cut-off frequency 2 Hz, upper Hz , full-wave rectification and smoothing Root Mean Square, window length ms.
For a proper comparison of activation levels of both muscles intra-individually special focus must be set on the standardization of the sEMG signals Burden, To put the activation levels of both muscles in relation to each other, reference values of both flexors were recorded during 5 s maximum voluntary isometric contraction measurements. Since sEMG amplitudes vary for different elbow angles, sEMG signals are standardized with the maximal amplitude in 90 degrees elbow flexion. Out of five MVC trials the mean of the best three with a minimum standard deviation and no significant differences in the maximal amplitude were chosen.
MVC was determined separately for every hand position and all signals were normalized to the according maximal value to account the contribution of muscle to hand position.
Main effects for each independent variable were investigated, and test statements were used to specify error terms. Statistical results were interpreted relative to biomechanical and biological significance. The mean solid lines and standard deviation dashed lines of all subjects were calculated for both muscles in different hand positions, shown in Figure 2.
Examining the muscular activity normalized to MVC, there are obvious differences in muscular coordination pattern during pronated elbow flexion in comparison to supinated and neutral hand position. As in pronated, the muscular activity of brachioradialis is constantly higher than in supinated and neutral hand position whereas the percentage activity of biceps brachii is nearly the same in all hand positions. The muscular activity of both muscles is constantly on the same level and slightly increasing with elbow joint angle in supinated and neutral hand position.
Figure 2. Mean solid lines and standard deviation dashed lines of the muscular activity of biceps brachii and brachioradialis from all subjects during elbow flexion in A neutral, B pronated, and C supinated hand position. The Post-hoc Tukey Test shows not only a general difference between the activation patterns of both elbow flexors with respect to hand position but additionally a significantly higher difference in pronated than in supinated and neutral hand position while the activity of biceps brachii remains constant.
Significant differences are found in pronated in comparison to supinated and neutral hand position in all considered intervals. Figure 3. Purpose of this study was the investigation of differing muscular contribution of biceps brachii and brachioradialis during elbow flexion with respect to hand position finding a reasonable explanation in a biomechanical disadvantaged role of biceps brachii as an elbow flexor in pronated hand position.
The function of brachioradialis has been discussed in literature with diverging results de Sousa et al. The presented results agree with most of the authors in the fact that brachioradialis is an active flexor of the elbow with increasing contribution in pronated hand position Jackson, ; de Sousa et al. Hereby it is important to consider that there may be an influence in brachioradialis' recruitment strategy depending on the biomechanical disadvantaged role of biceps brachii in pronation.
Therefore only an observation of the muscular activity of both muscles may lead to a useful interpretation. The results show clearly the function of brachioradialis as elbow flexor with a significant increased contribution in pronated hand position.
This can be concluded from the presented sEMG measurement in pronated hand position compared to neutral and supinated hand position, whereas the activation level of biceps brachii remains constant in all three hand position. From a biomechanical view brachioradialis has a longer anatomical lever arm than biceps brachii.
Consequently less muscular force than in biceps brachii is required to hold an external weight. However because of the longer lever arm brachioradialis demands a stronger contraction to flex the elbow and so a biomechanical disadvantage takes place.
So brachioradialis function is mainly lifting or holding an external weight, including the weight of the forearm like stated in Frisch and de Sousa et al. But in pronated hand position the biceps tendon is wrapped by its insertion in tuberosida radii Howard et al. Considering this fact, there is a biomechanical disadvantage of biceps brachii in pronated hand position to flex the elbow and the biomechanically advantaged brachioradialis takes over a higher contribution in elbow flexion because less muscle force can be generated by biceps brachii due to the disadvantaged lever arm at a constant activity.
These circumstances result in a significantly higher activity of brachioradialis to compensate the lower torque produced by biceps brachii although the activation level of biceps brachii is the same like in supinated and neutral hand position.
It should also be considered that there is neural inhabitation of biceps brachii and brachioradialis as stated in Naito et al. This may explain the similar activation level of both muscles in supinated and neutral hand position. The often discussed contribution of brachioradialis to pronation and supination cannot be proved by this study.
It should be mentioned that because of the normalization of the sEMG amplitudes to the specific MVC in every hand position, the contribution of biceps brachii and brachioradialis to pronation and supination movements are canceled in the processed normalized signals.
There is a strong influence of hand position on the inter-muscular coordination of biceps brachii and brachioradialis in elbow flexion. This has been shown by a significant increased muscular activity of brachioradialis during elbow flexion in pronated compared to supinated and neutral hand position whereas activity of biceps brachii remains constant.
This change in contribution of brachioradialis can be reasonable explained by the biomechanical disadvantaged role of biceps brachii in pronation resulting in brachioradialis taking a higher contribution in elbow flexion.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Amis, A. The elbow. PubMed Abstract Google Scholar. An, K. Muscles across the elbow joint: a biomechanical analysis. Boland, M. The function of brachioradialis.
Hand Surg. Burden, A. How should we normalize electromyograms obtained from healthy subjects? What we have learned from over 25 years of research. Deetjen, P. Munich: Urban and Fischer Verlag.
Electromyographic study of the brachioradialis muscle. Frisch, H. Programmierte Therapie am Bewegungsapparat. Google Scholar. Funk, D. Electromyographic analysis of muscles across the elbow joint. Hermens, H. Development of recommendations for SEMG sensors and sensor placement procedures.
Howard, J. Relative activation of two human elbow flexors under isometric conditions: a cautionary note concerning flexor equivalence. Brain Res. Jackson, C. Human anatomy. Philadelphia, PA: P. Blakiston's Son and Company. Naito, A. Electrophysiological studies of muscles in the human upper limb: the biceps brachii. Inhibitory projection from brachioradialis to biceps brachii motoneurones in human.
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