The role of exercising muscle length in the protective adaptation to a single bout of eccentric exercise.

The purpose of this study was to determine if the protective adaptation to a single bout of eccentric exercise (repeated bout effect) is dependent on the muscle length at which the eccentric contractions are performed. Ten subjects (six men, four women) performed two bouts of 120 isokinetic eccentric contractions separated by 2 weeks (target intensity was 90% of maximum isometric strength at 70 degrees). In the initial bout one limb exercised from 30 degrees to 70 degrees of knee flexion (short initial bout; SIB) and the contralateral limb exercised from 70 degrees to 110 degrees (long initial bout; LIB). For the repeated bout 2 weeks later, the limb that initially exercised at a short length now exercised at a long length (long repeated bout; LRB) and the limb that initially exercised at a long length now exercised at a short length (short repeated bout; SRB). Isometric strength and pain (scale 0-10) were assessed immediately post exercise and on the next 3 days. Strength loss and pain were greater following LIB versus SIB (strength loss P < 0.01; pain P < 0.001) and following LRB versus SRB (strength loss P < 0.01; pain P < 0.001). Strength loss and pain were not different between LIB and LRB. Pain was significantly greater following SIB compared with SRB (P < 0.05). Strength loss was not different between SIB and SRB. These results confirm that the symptoms of muscle damage are highly dependent on exercising muscle length and also demonstrate that the repeated bout effect is dependent on muscle length. Performing an initial bout of eccentric exercise at a shortened muscle length did not protect against strength loss and pain following a repeated bout at a longer muscle length. Data are given as mean (SE) unless otherwise stated.