Abstract
The purposes of this study were to investigate the muscle-tendon unit stiffness response and to compare the stiffness with those of other indirect markers induced by two bouts of unaccustomed eccentric exercise. Eleven untrained men performed two bouts of 200 maximal eccentric contractions of the right quadriceps 4 weeks apart. Changes in stiffness, pain evoked by stretching and pressure, plasma creatine kinase (CK) activity, and muscle thickness were followed for 7 days after each bout. Stiffness and pain peaked immediately and 1 day after the first exercise bout, whereas CK and thickness were highest 4 and 7 days after the first exercise bout, respectively (p < 0.05 for all). Muscular pain, thickness, and stiffness responses were lower by 53.3%, 99%, and 11.6%, respectively, after the repeated bout compared to after the first bout (p < 0.05 for all), while CK activity response did not differ significantly between bouts. High responders for an increase in muscle-tendon unit stiffness showed a repeated-bout effect for stiffness, pain, and CK activity (by 29%, 65%, and 98%, p < 0.05 for all), but the repeated-bout effect was not that clear in low responders. These findings suggest that a repeated eccentric exercise bout effect on stiffness in quadriceps is mostly not associated with muscle pain and CK activity, but there are large individual differences.
Highlights
In our earlier study of the interrelationships between muscletendon unit (MTU) stiffness, muscle pain and tenderness, swelling, and plasma creatine kinase (CK) release after acute eccentric exercise of the elbow flexors, we found strong correlations between muscle pain in response to stretching and increased resting elbow angle, and between peak plasma CK activity and the extent of swelling [4]
We aimed to examine the dynamics of active stretch-induced muscle pain, pressure-evoked pain, swelling, CK release, and passive MTU stiffness after the first and repeated bout of eccentric exercise of the knee extensors
Changes in MTU stiffness were minor associated with muscle pain and plasma CK activity
Summary
Muscle stiffening and delayed-onset muscle soreness (DOMS) are typical sensations experienced soon after unaccustomed eccentric exercise [1]. The asynchronous development of swelling and stiffness suggests that they may not be causally linked [3]. Our recent study showing that postexercise stiffness develops much earlier than swelling [4] provided evidence that questions the early claim that these two processes are interrelated and instead suggested that they are likely to be two aspects of the same phenomenon. In our earlier study of the interrelationships between muscletendon unit (MTU) stiffness, muscle pain and tenderness, swelling, and plasma CK release after acute eccentric exercise of the elbow flexors, we found strong correlations between muscle pain in response to stretching and increased resting elbow angle, and between peak plasma CK activity and the extent of swelling [4]
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