Size–strength relationships of the elbow flexors and extensors are not affected by age or gender

Torque-producing capacity is affected by moment arm in the human knee extensors

Objective

The torque-producing capacity can be assessed as maximal isometric torque per muscle size. Nevertheless, the factors contributing to this capacity remain poorly understood. In general, the magnitude of joint torque production is determined not only by muscle size but also by joint moment arm (MA). Based on this background, we hypothesized that longer MA would be related to higher torque-producing capacity despite a given muscle size. To test this hypothesis, we examined the relationship between MA and toque-producing capacity in the knee extensors. The quadriceps femoris muscle volume (MV) and knee extensor MA in 30 healthy young men were measured using magnetic resonance imaging. The knee extensor isometric torque was measured using a dynamometer. The knee extensor torque-producing capacity was calculated as the knee extensor isometric torque per quadriceps femoris MV.

Results

The quadriceps femoris MV and knee extensor MA correlated significantly with the knee extensor isometric torque (r = 0.785 and 0.790, respectively, both Ps < 0.001). Furthermore, the knee extensor MA correlated significantly with the knee extensor torque-producing capacity (r = 0.635, P < 0.001). These findings suggest that longer MA is an important factor for achieving higher torque-producing capacity in the human knee extensors.

Effect of maturation on muscle quality of the lower limb muscles in adolescent boys

Background

The purpose of this study was to clarify the effect of maturation on the muscle quality of the lower limb muscles around puberty.

Methods

Subjects were 117 Japanese boys age 12 to 15 years. The maturity status was assessed by using a self-assessment of stage of pubic hair development based on the criteria of Tanner. On the basis of the criteria, subjects were divided into the prepubescent or pubescent group. Muscle thickness of knee extensors and plantar flexors were measured by a B-mode ultrasound. Muscle volume index (MV) was calculated from muscle thickness and limb length. Maximal voluntary isometric joint toques (TQ) of knee extension and ankle plantar flexion were measured using a myometer. Muscle quality was derived from dividing TQ by MV (TQ/MV).

Results

In both muscles, TQ-MV relationships were also similar between the prepubescent and pubescent groups, and there was no significant difference in TQ/MV between the two groups when chronological age was statistically adjusted.

Conclusion

The current results indicate that, for adolescent boys, the muscle quality of the lower limb muscles is not significantly influenced by maturation.

Relationship between muscle architecture and joint performance during concentric contractions in humans

The purpose of this study was to examine the relationship between muscle architecture of the triceps brachii (TB) and joint performance during concentric elbow extensions. Twenty-two men performed maximal isometric and concentric elbow extensions against various loads. Joint torque and angular velocity during concentric contractions were measured, and joint power was calculated. Muscle length, cross-sectional areas, and volume of TB were measured from magnetic resonance images. Pennation angle (PA) of TB at rest was determined by ultrasonography. The PA was significantly correlated with the maximal isometric torque (r = .471), but not to the torque normalized by muscle volume (r = .312). A significant correlation was found between PA and the angular velocity at 0 kg load (r = .563), even when the angular velocity was normalized by the muscle length (r = .536). The PA was significantly correlated with the maximal joint power (r = .519), but not with the power normalized by muscle volume (r = .393). These results suggest that PA has a positive influence on the muscle shortening velocity during an unloaded movement, but does not have a significant influence on the maximum power generation in untrained men.