Muscle soreness and creatine kinase activity after eccentric actions: a cluster analysis

INTRODUCTION:

Maximal eccentric exercise promotes decreases in muscular strength, increases in delayed-onset muscle soreness (DMIT) and leakage of creatine kinase (CK) in the blood. However, these responses to eccentric exercise demonstrated large inter-individual variability.

OBJECTIVES:

To classify and analyze these responses according to individual vulnerability through the magnitude of the reduction of strength following eccentric exercise.

METHODS:

Eighteen healthy subjects (11 men and seven women aged 18 to 71 years) performed five sets of six maximal isokinetic eccentric actions of the elbow flexors using an isokinetic dynamometer (90°s^{- 1}, range of motion 80-20°). Maximum voluntary concentric muscle contraction (CVM), DMIT and CK pre-, post (except CK), 24h, 48h, 72h and 96h were analyzed after the protocol. Individuals were classified as "low" (BR) and "high" (AR) responders at the peak of CVM decrease post-exercise using a k-means cluster analysis and compared between groups for CVM, DMIT and CK with independent t-test.

RESULTS:

The comparison between BR and AR showed higher CVM decrease for AR (AR: -30.7±3.3%, BR: -14.1±2.2%, p<0.001) and higher DMIT also for AR group (AR: 33.0±8.6 mm; BR: 10.2±2.5 mm, p=0.033) however, the peak values of CK activity did not differ between groups (AR: 232.1±54.8 UI.L^{- 1}, BR: 306.1±82.3 UI.L^{- 1}, p=0.490).

CONCLUSION:

The classification of the subjects into low and high responders groups was important to demonstrate that the most responsive group to strength decrease after eccentric exercise also shows higher DMIT levels; notwithstanding, for creatine kinase this relation could not be established.

exercise; muscle strength; skeletal muscle; resistance training