EXPERIMENTAL STUDY ON INFLUENCE OF MUSCLE TENSION TOWARDS THE FUNCTION OF THE SKELETAL MUSCLE FOLLOWING ITS REINNERVATION

Objective To investigate the influence of tension on the function of the denervated skeletalmuscle after its reinnervation. Methods Fifty-four Sprague-Dawley (SD) rats were randomly divided into 3 groups. The left gastrocnemius muscles of the rats were dissected with only the neurovascular pedicles intact; the tib-ial nerves were cut and immediately repaired by epineurial suture. Then the Achilles tendons were isolated and treated accordingly; the Achilles tendon was lengthened by 0. 5cm in lengthened group, shortened by 0. 5cm in shortened group and left alone in normal (control) group. In the 2nd, 4th and 8th week after operation, the isometric twitch contractile force of both the right and the left gastrocnemius muscles were measured; specimens were taken from gastrocnemius muscle for histological study by light microscope. Results In comparison between the groups, the gastrocnemius muscles in the shortened group showed less severe muscle atrophy and connective tissue proliferation, bigger diameter and cross section dimension of the muscle fiber and greater isometric twitch contractile strength of the bilateral gastrocnemius muscles than those in the normal and lengthened groups in all the postoperative periods. Conclusion A proper high tension of the muscle may improve the function of the denervated skeletal muscle after its reinnervation.

Stiffness of individual quadriceps muscle assessed using ultrasound shear wave elastography during passive stretching

Background: Until recently it has not been possible to isolate the mechanical behavior of individual muscles during passive stretching. Muscle shear modulus(an index of muscle stiffness) measured using ultrasound shear wave elastography can be used to estimate changes in stiffness of an individual muscle. The aims of the present study were(1) to determine the shear modulus—knee angle relationship and the slack angle of the vastus medialis oblique(VMO), rectus femoris(RF), and vastus lateralis(VL) muscles;(2) to determine whether this differs between the muscles.Methods: Nine male rowers took part in the study. The shear modulus of VMO, RF, and VL muscles was measured while the quadriceps was passively stretched at 3°/s. The relationship between the muscle shear modulus and knee angle was plotted as shear modulus—knee angle curve through which the slack angle of each muscle was determined.Results: The shear modulus of RF was higher than that of VMO and VL when the muscles were stretched over 54°(all p < 0.01). No significant difference was found between the VMO and VL(all p > 0.05). The slack angle was similar among the muscles: 41.3°± 10.6°, 44.3°± 9.1°, and 44.3°± 5.6° of knee flexion for VMO, RF, and VL, respectively(p = 0.626).Conclusion: This is the first study to experimentally determine the muscle mechanical behavior of individual heads of the quadriceps during passive stretching. Different pattern of passive tension was observed between mono-and bi-articular muscles. Further research is needed to determine whether changes in muscle stiffness are muscle-specific in pathological conditions or after interventions such as stretching protocols.

Relationships among hamstring muscle optimal length and hamstring flexibility and strength

Background:Hamstring muscle strain injury(hamstring injury) due to excessive muscle strain is one of the most common injuries in sports.The relationships among hamstring muscle optimal lengths and hamstring flexibility and strength were unknown,which limited our understanding of risk factors for hamstring injury.This study was aimed at examining the relationships among hamstring muscle optimal length and flexibility and strength.Methods:Hamstring flexibility and isokinetic strength data and three-dimensional kinematic data for hamstring isokinetic tests were collected for11 male and 10 female recreational athletes.The maximal hamstring muscle forces,optimal lengths,and muscle lengths in standing were determined for each participant.Results:Hamstring muscle optimal lengths were significantly correlated to hamstring flexibility score and gender,but not to hamstring strength.The greater the flexibility score,the longer the hamstring muscle optimal length.With the same flexibility score,females tend to have shorter hamstring optimal muscle lengths compared to males.Hamstring flexibility score and hamstring strength were not correlated.Hamstring muscle optimal lengths were longer than but not significantly correlated to corresponding hamstring muscle lengths in standing.Conclusion:Hamstring flexibility may affect hamstring muscle maximum strain in movements.With similar hamstring flexibility,hamstring muscle maximal strain in a given movement may be different between genders.Hamstring muscle lengths in standing should not be used as an approximation of their optimal lengths in calculation of hamstring muscle strain in musculoskeletal system modeling.