Early Detection of Prolonged Decreases in Maximal Voluntary Contraction Force after Eccentric Exercise of the Knee Extensors

Purpose We examined whether the magnitude of muscle damage indicated by changes in maximal voluntary isometric contraction (MVIC) strength 1 to 3 d after unaccustomed eccentric exercise (ECC) was correlated with changes in central and peripheral neuromuscular parameters immediately post-ECC. Methods Twenty participants (19-36 yr) performed six sets of eight eccentric contractions of the knee extensors. Rate of force development (RFD) during knee extensor MVIC, twitch force, rate of force development (RFDRT) and rate of relaxation (RRRT) of the resting twitch, maximal M-wave (M-MAX), voluntary activation, silent period duration, motor-evoked potentials (MEP) and short-interval intracortical inhibition were assessed before, immediately after, and 1 to 3 d post-ECC. Relationships between changes in these variables immediately post-ECC and changes in MVIC strength at 1 to 3 d post-ECC were examined by Pearson product-moment (r) or Spearman correlations. Results Maximal voluntary isometric contraction strength decreased (-22.2% +/- 18.4%) immediately postexercise, and remained below baseline at 1 (-16.3% +/- 15.2%), 2 (-14.7% +/- 13.2%) and 3 d post-ECC (-8.6% +/- 15.7%). Immediately post-ECC, RFD (0-30-ms: -38.3% +/- 31.4%), twitch force (-45.9% +/- 22.4%), RFDRT (-32.5% +/- 40.7%), RRRT (-38.0% +/- 39.7%), voluntary activation (-21.4% +/- 16.5%) and MEP/M-MAX at rest (-42.5% +/- 23.3%) also decreased, whereas the silent period duration at 10%-MVIC increased by 26.0% +/- 12.2% (P < 0.05). Decreases in RFD at 0 to 30 ms, 0 to 50 ms, and 0 to 100 ms immediately post-ECC were correlated (P < 0.05) with changes in MVIC strength at 1 d (r = 0.56-0.60) and 2 d post-ECC (r = 0.53-0.63). Changes in MEP/M-MAX at 10%-MVIC immediately post-ECC were correlated with changes in MVIC strength at 1 d (r = -0.53) and 2 d (r = -0.54) post-ECC (P < 0.05). Conclusions The magnitude of decrease in MVIC strength at 1 to 3 d after ECC was associated with the magnitude of changes in RFD and MEP/M-MAX immediately post-ECC. However, based on individual data, these markers were not sensitive for the practical detection of muscle damage.

Automated summary

This study aimed to investigate whether the changes in maximal voluntary isometric contraction (MVIC) strength 1 to 3 days after unaccustomed eccentric exercise (ECC) were correlated with changes in central and peripheral neuromuscular parameters immediately post-ECC. The results indicated that the changes in rate of force development (RFD) and motor-evoked potentials (MEP)/maximal M-wave (M-MAX) immediately post-ECC were associated with the magnitude of decrease in MVIC strength at 1 to 3 days post-ECC. However, these markers were not sensitive for the practical detection of muscle damage based on individual data.