Effects of immediate vs. delayed massage-like loading on skeletal muscle viscoelastic properties following eccentric exercise

Background This study compared immediate versus delayed massage-like compressive loading on skeletal muscle viscoelastic properties following eccentric exercise. Methods Eighteen rabbits were surgically instrumented with peroneal nerve cuffs for stimulation of the tibialis anterior muscle. Rabbits were randomly assigned to a massage loading protocol applied immediately post exercise (n = 6), commencing 48 h post exercise (n = 6), or exercised no-massage control (n = 6). Viscoelastic properties were evaluated in vivo by performing a stress-relaxation test pre- and post-exercise and daily pre- and post-massage for four consecutive days of massage loading. A quasi-linear viscoelastic approach modeled the instantaneous elastic response (AG₀), fast (g₁^p) and slow (g₂^p) relaxation coefficients, and the corresponding relaxation time constants τ₁ and τ₂. Findings Exercise increased AG₀ in all groups (P < 0.05). After adjusting for the three multiple comparisons, recovery of AG₀ was not significant in the immediate (P = 0.021) or delayed (P = 0.048) group compared to the control group following four days of massage. However, within-day (pre- to post-massage) analysis revealed a decrease in AG₀ in both massage groups. Following exercise, g₁ ^p increased and g₂^p and τ₁ decreased for all groups (P < 0.05). Exercise had no effect on τ₂ (P > 0.05). After four days of massage, there was no significant recovery of the relaxation parameters for either massage loading group compared to the control group. Interpretation Our findings suggest that massage loading following eccentric exercise has a greater effect on reducing muscle stiffness, estimated by AG₀, within-day rather than affecting recovery over multiple days. Massage loading also has little effect on the relaxation response.