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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The purposes of the present study were (a) to determine whether a self-reported dominant leg was consistent with a dominant leg of force generation by using the isometric mid-thigh pull (IMTP) tests and (b) identify the features of bilateral IMTP (IMTPBi) and unilateral IMTP (IMTPUni) in terms of detecting strength imbalance of athletes. Fifteen male collegiate athletes performed IMTPUni and IMTPBi. The ground reaction force and surface electromyography were sampled with 1000Hz to assess force generation and neuromuscular activities in the gluteus maximus (Gmax), gluteus medius (Gmed), semitendinosus (ST), biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL) during IMTP. Legs were separated into dominant and non-dominant leg categories in accordance with two types of definitions including selfreported dominance of kicking leg and dominance of force generation in IMTP. In force generation and neuromuscular activity of IMTPBi and IMTPUni, there was no significant difference between self-reported dominant and non-dominant leg. However, results for a self-reported dominant leg were not consistent with results for dominant leg determined by force generation. In addition, the dominant leg of force generation exerted significantly larger PF than nondominant leg, and the magnitude of asymmetry in IMTPBi was significantly larger than that of IMTPUni. Moreover, in IMTPBi, the neuromuscular activity of the VL of the dominant leg of force generation was significantly larger than that of the non-dominant leg. Therefore, it was suggested the necessity to distinguish the two types of IMTP tests because of the possibility that the strength imbalances detected by IMTPBi and IMTPUni would have different connotations.

The purpose of the present study was to look at lower extremity force generation and neuromuscular activation by comparing isometric mid-thigh pull in the unilateral stance (IMTPUni) and bilateral stance (IMTPBi), and identifying the characteristics of IMTPUni. Fifteen male collegiate athletes (age: 20.60 ± 1.50 years, height: 1.74 ± 0.05 m, mass: 69.04 ± 4.23 kg) performed IMTPUni and IMTPBi as multi-joint isometric exercise. Ground reaction force (GRF) was measured to assess force generation during IMTP. Surface electromyography (EMG) was used to measure neuromuscular activation in the gluteus maximus (Gmax), gluteus medius (Gmed), semitendinosus, biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL), which were represented as average rectified values (ARVs). The EMG of the muscles during IMTPUni was normalized by IMTPBi to compare relative change among muscles. The co-contraction index (CI) during IMTPUni was also calculated by using normalized EMG. As a result, IMTPBi was significantly higher in BF than IMTPUni. However, in IMTPUni, although only one leg contributed to produce force, GRF of IMTPUni reached 80% of neuromuscular activity relative to IMTPBi. While the neuromuscular activation of Gmax, Gmed, BF, RF and VL was significantly higher proportionately in IMTPUni compared to IMTPBi, neuromuscular activation was even greater in Gmax and Gmed. The co-contraction index (CI) was increased in IMTPUni. The features of neuromuscular activation during IMTPUni were similar to the single leg squat and step-up exercise examined in previous studies due to the necessity to support the body with a single leg.

This study aimed to compare the load characteristics of sprint interval training (SIT) according to 400-m sprint performance. Eight elite sprinters and ten sub-elite sprinters were separated according to 400-m sprint performance and participated in this study (age: 21.0 ± 2.5 years, height: 176.0 ± 4.0 cm, and body mass: 67.0 ± 5.3 kg). All subjects performed two different SIT protocols on a cycle ergometer. The SIT protocols consisted of two bouts of 20-s maximal sprints interspersed with either 30-s rest (R-30s) or 60-s rest (R-60s). Mean power output over both sprints in R-60s was significantly greater than in R-30s in both groups (p < 0.001). In the elite group, blood lactate did not significantly differ between R-30s and R-60s even though different mean power output was recorded. However, in the sub-elite group, blood lactate from the R-60s condition was significantly greater than from the R-30s condition (p < 0.05). These results indicate different physiological responses to SIT depending on 400-m sprint capabilities. To enhance anaerobic adaptations, it is suggested that elite 400-m sprinters should utilize SIT with very short recovery periods, while sub-elite 400-m sprinters should utilize relatively longer recovery periods