Abstract
Low-intensity training at long muscle-tendon unit lengths with a greater passive
force may cause muscle swelling, which may be related to hypertrophy, even if
the active force production is lower than that at short muscle-tendon unit
lengths. This study compared muscle swelling after low-intensity torque-matched
isometric exercises at long and short muscle-tendon unit lengths. Twenty-six
volunteers performed isometric knee flexion exercises (30% of maximal
voluntary contraction× 5 seconds×10
repetitions×9 sets) either at long or short lengths of the hamstrings
(90° hip flexion and 30° knee flexion, or 90° hip and
knee flexion, respectively). Active torque was calculated by subtracting passive
torque from the total torque generated during exercise. Swelling-induced changes
in cross-sectional area was assessed before and after exercise using
ultrasonography. There was no between-group difference in the total torque
during exercise; however, the active torque was significantly lower in the group
trained at long than in the group trained at short muscle-tendon unit lengths.
Muscle swelling occurred in both groups. The results suggest that exercise at
long muscle-tendon unit lengths can cause similar muscle swelling as exercise at
short muscle-tendon unit lengths, even in cases where active torque production
is lower than that at short lengths.
Key words
active torque - cross-sectional area - isometric training - muscle swelling - passive torque - ultrasonography
