The relationship between torque and joint angle during knee extension in boys and men

The length-tension relationship of muscle contraction is well documented in adults. However, research on this relationship in children has been limited. The aim of this study was to compare differences in the torque-joint angle relationship of the quadriceps muscle in children and adults. Eight boys aged 8-10 years and eight men aged 20-26 years performed two maximal voluntary isometric contractions at six knee joint angles (20 degrees, 40 degrees, 60 degrees, 80 degrees, 90 degrees, 100 degrees). The mean of the two trials was used as the performance measure. Both groups demonstrated an expected increase in relative torque as the joint angle increased (P< 0.05). The men produced significantly greater relative torque at 20 degrees, 40 degrees and 60 degrees knee flexion (P < 0.05). The percentage of maximal torque at these angles for the men and boys respectively were: 35.2+/-4.3 vs 15.2+/-12%, 63.6+/-9.1 vs 51.8+/-16.8% and 93.6+/-6.5 vs 84.4+/-14.4%. There were no group differences at 80 degrees or 90 degrees. Peak torque was attained at 80 degrees in men, but decreased significantly (P< 0.05) at 90 degrees and 100 degrees. For boys, peak torque was attained at joint angles of 80 degrees and 90 degrees. The reduction in peak torque at 100 degrees was not statistically significant, but the relative torque at this angle was lower in men than in boys (77.9+/-13.7 vs 87.1+/-10.4%; P< 0.05). In conclusion, the relationship between torque and joint angle appears to be affected by age.