Effects of carbon dioxide hydrate cryotherapy on knee flexor muscle function recovery trajectory after muscle damage: a randomized controlled trial.

Introduction: This study investigated the effects of carbon dioxide hydrate (CDH) cryotherapy on the recovery trajectories of muscle function and physiological markers following exercise-induced muscle damage (EIMD) of the knee flexors.

Methods: In a randomized parallel-group design, 24 young men were assigned to the CDH, conventional icing (ICE), or non-intervention control (CON) group (n = 8 per group). To induce muscle damage, participants performed 10 sets of eight maximal eccentric contractions of the knee flexors in a prone position (knee joint range: 75°-15° of flexion at 60°/s; 0° = the fully extended anatomical position). Maximal voluntary isometric contraction (MVIC) torque of the knee flexors was measured at 30° of knee flexion at baseline (PRE), immediately post-exercise (POST), and at 4.5, 24, 48, 72, and 168 h post-exercise. Secondary outcomes, including thigh circumference, hip joint range of motion (ROM), and hamstring muscle stiffness and pressure-induced soreness were assessed at all time points except POST. A 20-min intervention was administered after each assessment from POST to 72 h.

Results: Linear mixed-effects models, adjusted for PRE values, revealed no significant group × time interactions for changes from PRE in any outcome across post-exercise time points (POST to 168 h for MVIC torque; 4.5 to 168 h for secondary outcomes; p = 0.177-0.914). A significant main effect of group was observed only for hip joint ROM (p = 0.039). Post-hoc comparisons revealed a significantly greater overall reduction from PRE in the CDH group than in the CON group (difference: 10.3°, 95% CI: 3.0° to 17.6°, p = 0.017), with no significant differences between the other group pairs (both p = 0.131). Given the multi-outcome testing, this isolated effect should be interpreted as exploratory.

Conclusion: Under the present experimental conditions, CDH cryotherapy did not accelerate the recovery of muscle function or attenuate secondary markers following EIMD relative to conventional icing or no intervention.