Context: Each hamstring muscle is subdivided into several regions by multiple motor nerve branches, which implies each region has different muscle activation properties. However, little is known about the muscle activation of each region with a change in the knee joint angle. Understanding of regional activation of the hamstrings could be helpful for designing rehabilitation and training programs targeted at strengthening a specific region. Objective: To investigate the effect of knee joint angle on the activity level of several regions within the individual hamstring muscles during isometric knee-flexion exercise with maximal effort (MVCKF). Design: Within-subjects repeated measures. Setting: University laboratory. Participants: Sixteen young males with previous participation in sports competition and resistance training experience. Intervention: The participants performed 2 MVCKF trials at each knee joint angle of 30°, 60°, and 90°. Outcome Measures: Surface electromyography was used to measure muscle activity in the proximal, middle, and distal regions of the biceps femoris long head (BFlh), semitendinosus, and semimembranosus of hamstrings at 30°, 60°, and 90° of knee flexion during MVCKF. Results: Muscle activity levels in the proximal and middle regions of the BFlh were higher at 30° and 60° of knee flexion than at 90° during MVCKF (all: P < .05). Meanwhile, the activity levels in the distal region of the BFlh were not different among all of the evaluated knee joint angles. In semitendinosus and semimembranosus, the activity levels were higher at 30° and 60° than at 90°, regardless of region (all: P < .05). Conclusion: These findings suggest that the effect of knee joint angle on muscle activity level differs between regions of the BFlh, whereas that is similar among regions of semitendinosus and semimembranosus during MVCKF.

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Kawama, R, Takahashi, K, and Wakahara, T. Effect of hip joint position on electromyographic activity of the individual hamstring muscles during stiff-leg deadlift. J Strength Cond Res 35(2S): S38–S43, 2021—This study investigated the effect of hip joint position on the activity level of individual hamstring muscles during stiff-leg deadlift. Fourteen male collegiate sprinters performed stiff-leg deadlift in the adducted (ADD), neutral (NT), abducted (ABD), internally rotated by 20° (IN20), and externally rotated positions by 20° (EX20) and by 40° (EX40) of the hip joint. Surface electromyogram (EMG) was recorded from the proximal and distal regions of the biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM). Root mean square value of EMG (RMS-EMG) data were calculated for the concentric and eccentric phases of deadlift and was normalized by RMS-EMG during maximal voluntary contraction of isometric knee flexion as an activity level. Results revealed that the activity level of BFlh during the concentric phase was higher in EX20 (p = 0.008, difference = 6.3%) and EX40 (p = 0.001, difference = 9.4%) than in NT. Semimembranosus showed a higher activity level in IN20 than in EX40 during the concentric (p = 0.004, difference = 4.3%) and eccentric phases (p = 0.023, difference = 4.1%). In addition, the activity level was higher in ABD than in NT for BFlh (p = 0.015, difference = 4.6%), ST (p = 0.047, difference = 3.8%), and SM (p = 0.005, difference = 3.9%) during the concentric phase of deadlift. In conclusion, the deadlift in the hip-abducted position requires high activation of the individual hamstrings and that in the hip externally and internally rotated positions needs high activation of BFlh and SM, respectively.