Time-course effect of exercise-induced muscle damage on localized muscle mechanical properties assessed using elastography

AimChanges in muscle stiffness after exercise-induced muscle damage have been classically inferred from passive torque-angle curves. Elastographic techniques can be used to estimate the shear modulus of a localized muscular area. This study aimed to quantify the changes in shear elastic modulus in different regions of the elbow flexors after eccentric exercise and their relation to muscle length. MethodsShear elastic modulus and transverse relaxation time (T-2) were measured in the biceps brachii and brachialis muscles of sixteen participants, before, 1 h, 48h and 21days after three sets of ten maximal isokinetic eccentric contractions performed at 120 degrees s(-1). ResultsThe shear elastic modulus of the elbow flexors significantly increased 1h (+46%; P=0.005), with no significant change at 48h and 21D, post-exercise. In contrast, T-2 was not modified at 1h but significantly increased at 48h (+15%; P<0.05). The increase in shear elastic modulus was more pronounced at long muscle lengths and reached a similar extent in the different regions of the elbow flexors. The normalized hysteresis area of shear elastic modulus-length relationship for the biceps brachii increased 1h post-exercise (31%) in comparison with the pre-exercise value (18%), but was not significantly altered after five stretching cycles (P=0.63). ConclusionOur results show homogeneous changes in muscle shear elastic modulus within and between elbow flexors. The greater increase in shear elastic modulus observed at long muscle lengths suggests the putative involvement of both cross-bridges number and titin in the modifications of muscle shear elastic modulus after damaging exercise.