Background: Lengthening contractions (LC) are widely used to treat tendinosis and strength deficits in sports activities, training and muscle rehabilitation; yet, no studies have
compared its functional impact based on the contraction speed and examined changes in muscle performance variables (MP; peak torque, work and power) and delayed onset of muscle soreness (DOMS).
Therefore, the purpose of this study was to compare the changes induced by a session of slow (S:30°/s) vs. fast (F:120°/s) LC on MP and DOMS in healthy and physically active young men.
Methods:8 men were randomized to either S or F group. All subjects performed 200 isokinetic LC (20 sets, 10 reps) of the quadriceps of their dominant leg. Amount of work (W) and peak
torque (PT) per set in each group was calculated; MP and DOMS were assessed at baseline and 48h post-exercise. MP dependent variables were isometric and isokinetic (60°/s) PT, time to peak (isometric
and isokinetic) and W. Data were analyzed by paired and unpaired t-test for comparisons within each group and between groups, respectively. The Universidad Industrial de Santander Ethics Committee
approved the study.
Results: The average total W (1661J) and PT per set (172.8Nm) decreased over the 200 repetitions (p<0.001) in both groups. During exercise in the S-group the mean PT during sets 16-20
(135.7±3.4Nm) was 34.2% lower that PT from the first 5 sets (207.8±6.6, p=0.001). In the F-group the mean PT during sets 16-20 (146.4±2.2) was 33.5% lower than the first 5 sets (220±5, p<0.001).
However, there was a greater decrease in PT during the sets 16-20 in the S compared to F-group (p=0.04). The mean total W in the S-group during sets 16-20 (1298±32.9J) was 38.1% lower than the first 5
sets (2098±61.1J, p<0.001). In the F-group, the mean total W during the sets 16-20 (1334±15.1J) was 37.8% lower than the first 5 sets (2114.2±36J, p<0.001). No detectable differences during the
exercise bout were detected for mean total W per set between groups (p=0.3). Comparisons of MP and DOMS between baseline and 48h post within groups showed a decrease in isometric PT of 31.3% in the
S-group (pre:221,4±34,5Nm; 48h:152±21.5Nm,p=0.03), and 20.9% in the F-group (pre:194.4±23.5; 48h:153.8±31.7Nm,p=0.03). DOMS increased in the S-group from 5.3±2.5 to 35.5±16.6 mm 48h-post (p=0.01) and
from 0.8±1 to 28.7±19.5mm (p=0.03) in the F-group. The other MP variables did not show change after the exercise bout and no differences between groups were detected.
Conclusions:In spite of the muscle movement´s speed differences, our results indicate that MP and DOMS are affected by a single bout of LC. It has been described that motor units
recruitment occur differently based on the movement´s speed, also some muscle fiber types are more susceptible to damage induced by exercise; however, our findings do not show any impact of these
physiological differences on the muscle group performance.