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2003 Publications

Changes in the relationship between joint angle and torque production associated with the repeated bout effectby McHugh MP, Tetro DT. - last modified 2012-11-27 00:00
J Sports Sci. 2003 Nov;21(11):927-32.

 

A single bout of eccentric exercise induces a protective adaptation against damage from a repeated bout. The aim of this study was to determine whether this repeated bout effect is due to a change in the length-tension relationship.

Twelve individuals performed an initial bout of six sets of 10 eccentric quadriceps contractions and then performed a repeated bout 2 weeks later.

Eccentric contractions were performed on an isokinetic dynamometer at 1.04 rad x s(-1) with a target intensity of 90% of isometric strength at 70 degrees of knee flexion. Isometric strength and pain were recorded before and after both eccentric bouts and on each of the next 3 days. Isometric strength was tested at 30 degrees, 50 degrees, 70 degrees, 90 degrees and 110 degrees of knee flexion.

On the days following the initial bout, there was a significant loss of isometric strength at all knee flexion angles except 110 degrees (bout x angle: P < 0.01).

On day 2, strength averaged 86% of baseline for 30-90 degrees and 102% of baseline for 110 degrees. Strength loss and pain after the initial bout was contrasted by minimal changes after the repeated bout (pain: P < 0.001; strength: P < 0.01).

The repeated bout effect was associated with a rightward shift in the length-tension curve; before the repeated bout, isometric strength was 6.8% lower at 30 degrees and 13.6% higher at 110 degrees compared with values before the initial bout (bout x angle: P < 0.05).

Assuming that torque production at 110 degrees occurs on the descending limb of the length-tension curve, the increase in torque at 110 degrees may be explained by a longitudinal addition of sarcomeres.

The addition of sarcomeres would limit sarcomere strain for subsequent eccentric contractions and may explain the repeated bout effect observed here.