Effects of vibration and passive resting on muscle stiffness and restitution after submaximal exercise analyzed by elastography.

Purpose: The research aimed to assess the influence of vibration therapy on acceleration of muscles regeneration process after physical effort. Verification of the pace of motor capabilities recovery in fatigued muscles was performed with the use of the measurement method applying shear-wave elastography. It took into account an alteration in muscle stiffness affected by created passive stresses and accompanying deformations connected with muscles work above their resting length.

Methods: The research included 42 young males aged 20-24. They all were a homogeneous group regarding body build indices (body height 175.4 ± 8.1 cm; body mass 75.5 ± 8.32 kg) and the level of physical activity. Muscles of lower limbs (hip and knee joints extensors and flexors plantaris) were subject to submaximal exercise of the auxotonic muscle work character after a 90 s warm-up. The exercise comprised 20-fold overcoming the load at the level of 75% of maximal strength abilities without rest, by alternating between extension and flexion of lower limbs joints at the leg press placed at 45° angle upward and monitoring of angle setting of lower limbs joints. The post-exercise restitution used a vibration stimulus of variable frequency ranging from 20 to 50 Hz and amplitude of 0.5 mm, and passive resting in the control group. For an objective assessment of the applied vibration effect, a 5-fold measurement of rectus femoris muscles stiffness of both limbs at the middle of venter took place after each stage of the experiment.

Results: After warm-up, a considerable increase of the examined muscles stiffness, that did not vary significantly, was observed. In the DW experimental group (vibration massage), where post-exercise restitution was enhanced by vibration, significantly lower values of muscle stiffness were registered after each of the post-exercise regeneration stages in relation to the DB control group (passive rest). After the I regeneration stage, a value of the Δσ_r1-s variable ( p < 0.05) lower by 16% was noticed in favour of the group enhanced by vibration. Whereas, values of muscles stiffness after the II stage of regeneration, Δσ_r2-s were by 14% lower in favour of DW group ( p < 0.005).

Conclusions: Enhancement of the post-exercise relaxation of muscles by vibration treatment significantly lowered the values of post-exercise muscles stiffness and turned out to be a more effective method of restitution than passive resting. Recovery of the level of muscles stiffness from before the exercise was much slower in the control group than in the one enhanced by vibration. The improved method of muscle stiffness measurement with the use of shear-wave elastography with a special head attachment turned out to be a useful tool to assess post-exercise muscles restitution.