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

Abstract

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.

Relationship of The Knee Extensor Strength But Not The Quadriceps Femoris Muscularity With Sprint Performance in Sprinters: A Reexamination and Extension

“…Because muscle strength (i.e., joint torque) is theoretically expressed as the product of muscle force and MA dimension, the magnitude of the knee extensor strength is determined not only by the quadriceps femoris size but also by the knee extensor MA. Indeed, we and others previously reported a positive correlation between muscle strength and MA dimension of the knee extensors in untrained participants [10][11][12]; however, no study has examined such a relationship in sprinters. If this relationship is observed for sprinters, it may help our understanding of the present ndings that higher knee extensor strength was related to better 100-m sprint performance, potentially by enhancing knee extensor joint torque while sprinting, which is attributed to greater knee extensor MA rather than quadriceps femoris size.…”

“…The method for measuring the knee extensor strength has been described in our previous studies [11,12,15,16]. The isometric and isokinetic knee extensor strengths of the right leg were measured using a dynamometer (BIODEX system 3; BIODEX Medical, Shirley, NY, USA).…”

“…The rest intervals between the trials were set for 1 min. If the difference between the two strength values of each strength measurement was more than 5 % of the highest value, additional trials were performed until this was corrected, as our previous studies [11,12,15,16]. The highest value of the two trials, or more than two trials, for each strength measurement was used for analyses.…”

“…The method for measuring the quadriceps femoris size has been described in our previous studies [11][12][13]. The quadriceps femoris size was measured using a 1.5-T magnetic resonance system (Signa HDxt; GE Medical Systems, WI, USA).…”

“…Several previous studies reported a positive correlation between isokinetic knee extensor strength and sprint performance in sprinters [6,7]; however, further understanding of this relationship has not progressed in recent years. The magnitude of the muscle strength, including isokinetic strength, of the knee extensors is primarily determined by agonist quadriceps femoris size in untrained participants [10][11][12]; however, to the best of our knowledge, no study has examined such a relationship in sprinters. Despite this theoretical relationship, we and others previously determined no correlation between quadriceps femoris size and sprint performance in sprinters [13,14].…”