Comparison among three different intensities of eccentric contractions of the elbow flexors resulting in the same strength loss at one day post-exercise for changes in indirect muscle damage markers

Purpose: The present study compared three different intensity elbow flexor eccentric exercises resulting in the same magnitude of maximal voluntary isomeric contraction torque (MVC) decrease at 1 day post-exercise for changes in several indirect markers of muscle damage and proprioception. Methods: Sedentary young men performed eccentric contractions of the elbow flexors using a dumbbell corresponding to either 10%, 50% or 100% of MVC to induce ~ 20% decrease in MVC at 1 day post-exercise (n = 12/group). MVC, range of motion (ROM), upper arm circumference (CIR), muscle soreness, plasma creatine kinase (CK) activity, and proprioception measures (force match, joint position sense) were taken before to 5 days after exercise, and the changes were compared among the groups. Results: MVC and ROM recovered faster (P < 0.05) in the order of 10% (e.g., 3 days post-exercise: − 3 ± 4%, 0 ± 1%), 50% (− 12 ± 3%, − 3 ± 2%) and 100% group (− 16 ± 4%, − 5 ± 1%). Peak CIR, muscle soreness and CK activity were smaller for 10% (Δ3 ± 1 mm, 26 ± 10 mm, 1049 ± 316 IU/L) than 50% (Δ6 ± 2 mm, 36 ± 14 mm, 1473 ± 429 IU/L) and 100% groups (Δ8 ± 2 mm, 47 ± 15 mm, 2104 ± 929 IU/L). The proprioception measures recovered faster (P < 0.05) for 10% followed by 50% then 100% group. The recovery rate of MVC from immediately to 1 day post-exercise was correlated (P < 0.05) with the changes in the muscle damage and proprioception markers. Conclusion: These results suggest that the MVC at 1 day post-exercise does not necessarily predict the changes in muscle damage markers in the following days, but the MVC recovery rate in the first 24 h reflects the magnitude of muscle damage better.