Proximal vs. Distal Fascicle Behavior within the Biceps Femors Long Head at Different Muscle Activation Levels

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)
Hunter Bennett (Creator)
East Carolina University (ECU )
Web Site:
Anthony Kulas

Abstract: Hamstring strains have been shown to occur more often in the long head of the biceps femoris (BFLH) than the semitendinosus and semimembranosus with most injuries occurring in the proximal half of the BFLH. Muscle modeling has shown significantly greater tissue strains in the more proximal regions compared to more the distal regions of the BFLH. These data suggest there are regional differences in fascicle behavior between the proximal and distal fascicles of the BFLH during contractions. The purpose of this study was to assess the magnitude of shortening of the proximal and distal fascicles in the long head of the biceps femoris under different muscle activation levels. This study tested the hypotheses that 1) the proximal fascicles will be longer and 2) the proximal fascicles will undergo greater shortening than the distal fascicles when the muscle is at various activation levels. Subjects were 11 young (age: 21.3±1.8 yrs. height: 167.9±10.0 m and mass 65.9±10.6 kgs.) males and females who resistance trained and were non-collegiate athletes. Longitudinal ultrasound images were taken of the BFLH at rest (hip and knee at 0°°) and during sustained isometric contraction levels of 10 25 50 and 75% MVIC while prone on a dynamometer with hip and knee flexed to 45°°. BFLH and ST/SM activation during ramp trials were correlated and used to predict BFLH activation during subsequent submaximal trials. Through a combination of linear regression analyses and repeated measures ANOVAs the results showed that the proximal fascicles were longer (3.24 cm P<.001) and shortened ~44% more than their distal counterparts on an absolute level (P<.001). The presence of a region by condition interaction also showed the proximal fascicles had significant incremental shortening from the passive to 50.4% activation while the distal fascicles only had significant incremental shortening from passive to 20.6% activation (P<.05). Once normalized to the resting lengths the analysis of strain showed both regions underwent significant shortening (P<.001) however the proximal fascicles did not undergo more shortening than the distal fascicles (P=.72). The results of the group data do not agree with heterogeneous architecture behavior in previous literature. However qualitative analyses of individual subjects show the presence of two types of heterogeneous regional fascicle behavior that was not present when averaged as a group. Some subjects showed greater strain magnitudes in the proximal or distal regions while some subjects had seemingly equal amounts of strain in both regions. Also some subjects reached much higher magnitudes of strains than other subjects ranging from .09 to .33. In conclusion the data support our first hypothesis that the absolute lengths of the proximal fascicles are longer and shorten more than the distal fascicles. The proximal fascicles had greater absolute shortening however once normalized to resting fascicle length the proximal fascicles did not undergo more strain than the distal fascicles i.e. the behavior differences between regions was not present in strain measurements. Thus our second hypothesis was supported by the absolute length changes but rejected by the normalized length changes. The "qualitative" individual subject heterogeneity depicts the need for further investigation on the possibility of strain variability between subjects and within the BFLH itself as well as the need for this type of investigation during more dynamic movements. Further knowledge of this commonly strained muscle's regional behavior during dynamic movements could provide clinical evidence of proximal hamstring strain predisposition. 

Additional Information

Date: 2013
Kinesiology, Physiology, fascicles, hamstrings, heterogeneity, strains

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