The effect of an inclined landing surface on biomechanical variables during a jumping task
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Changes in the relationship between joint angle and torque production associated with the repeated bout effect
by
McHugh MP, Tetro DT.
—
last modified
2009-10-09 15:16
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.