Heat Shock Proteins as Markers of Contraction‐Induced Muscle Damage

Angular contraction velocity has been proposed as a determinant in the severity of lengthening contraction‐induced muscle damage, yet empirical evidence is equivocal. We measured heat shock protein (HSP) content as a marker of muscle damage severity following lengthening contractions (LCs) at multiple angular velocities (slow; 63°/sec, medium; 127°/sec, fast; 190°/sec) to determine the relationship between angular velocity and muscle damage. To do this, male sprague‐dawley rats were anaesthetized and one tibialis anterior (TA) muscle was subjected to 60 LCs (3 sets of 20 LCs with 5 minutes rest between sets) at three velocities, while the contralateral TA served as a control. Twenty‐four hours after the last LC, intramuscular Hsp72 content, as assessed by western blotting, was significantly (p<0.001) increased in the stimulated TA regardless of the angular velocity. Similarly, Hsp25 content was also elevated but only considered significant (p<0.05) after LCs at the slow velocity (63°/sec). Interestingly, TA muscle function (ability to generate torque) was affected greatest following slow LCs. When compared to fast LCs (190°/sec), slow LCs caused significantly (p<0.05) greater loss of muscle torque with each set of 20 LCs, suggesting muscle damage and/or fatigue was greater after slow LCs. However, histological assessment of TA cross‐sections suggest the severity of muscle damage (measured as necrotic fibers and inflammatory infiltrates) and metabolic fatigue (measured as glycogen depletion) was similar between velocities. Taken together, the results suggest Hsp72 content may be a novel marker for determining the severity of LC‐induced muscle damage. Support or Funding Information No external funding