Functional difference between the proximal and distal compartments of the semitendinosus muscle

The anatomical, electrophysiological and histological observations of muscle contraction units in rabbits: a new perspective on nerve injury and regeneration

In the conventional view a muscle is composed of intermediate structures before its further division into microscopic muscle fibers. Our experiments in mice have confirmed this intermediate structure is composed of the lamella cluster formed by motor endplates, the innervating nerve branches and the corresponding muscle fibers, which can be viewed as an independent structural and functional unit. In this study, we verified the presence of these muscle construction units in rabbits. The results showed that the muscular branch of the femoral nerve sent out 4–6 nerve branches into the quadriceps and the tibial nerve sent out 4–7 nerve branches into the gastrocnemius. When each nerve branch of the femoral nerve was stimulated from the most lateral to the medial, the contraction of the lateral muscle, intermediate muscle and medial muscle of the quadriceps could be induced by electrically stimulating at least one nerve branch. When stimulating each nerve branch of the tibial nerve from the lateral to the medial, the muscle contraction of the lateral muscle 1, lateral muscle 2, lateral muscle 3 and medial muscle of the gastrocnemius could be induced by electrically stimulating at least one nerve branch. Electrical stimulation of each nerve branch resulted in different electromyographical waves recorded in different muscle subgroups. Hematoxylin-eosin staining showed most of the nerve branches around the neuromuscular junctions consisted of one individual neural tract, a few consisted of two or more neural tracts. The muscles of the lower limb in the rabbit can be subdivided into different muscle subgroups, each innervated by different nerve branches, thereby allowing much more complex muscle activities than traditionally stated. Together, the nerve branches and the innervated muscle subgroups can be viewed as an independent structural and functional unit. This study was approved by the Animal Ethics Committee of Peking University People’s Hospital (approval No. 2019PHE027) on October 20, 2019.

Effects of Vastus Lateralis Muscle Fascicle Length on Isokinetic Muscular Strength and Physical Fitness in Collegiate Athletes

OBJECTIVES The purpose of this study was to examine the effects of vastus lateralis muscle fascicle length on isokinetic muscle strength and physical fitness in collegiate athletes.METHODS 32 male collegiate athletes were classified into short fascicle length group (SFG, n=16) and long fascicle length group (LFG, n=16) by ultrasonic imaging. Both groups were tested for isokinetic muscular strength (peak torque, angle of peak torque and time to peak torque) and physical fitness (20 m sprint, T-drill, reaction time, side hop, square hop, figure of 8 hop, sergeant jump and Y-balance).RESULTS LFG showed a positive effect on pennation angle (<i>p</i>=.001), fascicle length (<i>p</i>=.001), angle of peak torque at 180°/sec (<i>p</i>=.037), time to peak torque at 90°/sec and 180°/sec (<i>p</i>=.036; <i>p</i>=.039), 20 m sprint (<i>p</i>=.016), T-drill (<i>p</i>=.005), side hop (<i>p</i>=.001) and square hop (<i>p</i>=.001), respectively compared to SFG. However, there was no difference between both groups of peak torque at 30°/sec, 90°/sec and 180°/sec, angle of peak torque at 30°/sec and 90°/sec, time to peak torque at 30°/sec, reaction time, sergeant jump and Y-balance.CONCLUSIONS These results found that long fascicle length of vastus lateralis muscle have excellent isokinetic muscle strength and physical fitness in collegiate athletes.

Muscle Recruitment Pattern of the Hamstring Muscles in Hip Extension and Knee Flexion Exercises

We aimed to compare dynamic exercise performance between hip extension exercises with different knee angles and between knee flexion exercises with different hip angles, and to investigate the recruitment pattern of the hamstrings in each exercise. Seven men performed 4 isokinetic exercises (3 maximal concentric contractions at 30°/s (peak torque) and 30 maximal concentric contractions at 180°/s (total work)): hip extension with the knee fully extended (HEke) and with the knee flexed at 90° (HEkf) and knee flexion with the hip fully extended (KFhe) and with the hip flexed at 90° (KFhf). The recruitment pattern of the hamstrings was evaluated in each exercise using magnetic resonance imaging (T2 calculation). The HEke condition showed significantly greater peak torque than the HEkf condition (p < 0.05). The KFhf condition had significantly greater peak torque and total work values than the KFhe condition (p < 0.05). Although the biceps femoris long head, semitendinosus, and semimembranosus had significantly increased post-exercise T2 values in the HEke (p < 0.05), KFhe, and KFhf conditions (p < 0.01), the T2 increase values were significantly greater under the KFhf than the HEke condition (p < 0.05). The semitendinosus showed a significantly greater T2 increase value than other muscles under both KFhe and KFhf conditions (p < 0.05). Performance of hip extension and knee flexion exercises increases when the hamstring muscles are in a lengthened condition. The hamstring muscles (particularly the semitendinosus) are more involved in knee flexion than in hip extension.