Changes in heat shock proteins (HSPs), HSP27 and HSC/HSP70 were characterized in human biceps brachii muscle following damaging high-force eccentric exercise. Male and female volunteers performed a maximal eccentric resistance exercise with the elbow flexor muscles of the non-dominant arm known to be sufficient to cause substantial muscle damage. Protein extracts of biopsy tissue samples taken 48 h post-exercise were immunoblotted for HSC/HSP70 and HSP27. Densitometric analysis demonstrated that these proteins increased significantly (P < 0.01) in the damaged biceps brachii relative to the control arm. The HSC/HSP70 increased 1064% in the exercised sample while HSP27 increased by 234%. Although the literature reports a muscular heat shock response following aerobic, oxidative exercise, this is the first documentation of increases in protein expression of both HSC/HSP70 and HSP27 in human skeletal muscle in response to a single bout of resistance exercise.
These data indicate that the PX HSP and mitogen-activated protein kinase responses are exercise-specific and local, not systemic. Further, only the resistance exercise induced HSP expression (protein and mRNA) and JNK/ERK activation at 48 h PX, suggesting that these molecules may be important to long-term skeletal muscle adaptations such as hypertrophy.
Exercise-induced damage significantly and predictably alters indirect indicators of muscle damage after one bout of damaging exercise but this response is dampened following a second bout of the same exercise performed 1-6 weeks later. Previously we have described a marked increase in the levels of heat shock proteins (HSPs) HSP27 and HSP70 in human biceps muscle following one bout of high-force eccentric exercise. The purpose of the present study was to examine the intramuscular HSP27 and HSP70 response following two identical bouts of exercise [bout 1 (B1) and bout 2 (B2), separated by 4 weeks] relative to indirect indices of muscle damage. Ten human subjects performed 50 high-force eccentric contractions with their non-dominant forearm flexors; muscle damage of the biceps brachii was evaluated 48 h post-exercise with indirect indices [serum creatine kinase (CK) activity, soreness, isometric maximal voluntary contraction (MVC) force and relaxed arm angle] and immunoblotting of high ionic strength muscle biopsy extracts for both HSPs. Not unexpectedly, the indirect indicators of damage changed dramatically and significantly (P < 0.01) after B1 but had a much smaller response after B2. The magnitude of the HSP response was the same after both bouts of exercise, though the control and exercised samples of B2 demonstrated a lower basal HSP expression. Thus, though both indirect and cellular indicators of exercise-induced muscle damage demonstrate an adaptation consequent to the first bout of exercise, these adaptations are quite different. It is possible that the lower basal HSP expression of the cellular response mediates the attenuation of damage associated with B2 as indicated by indirect indices.
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