Calf Muscle Strength in Humans

In an effort to measure strength characteristics of the calf muscles, 18 subjects (14 male, 4 female, age = 34.3 ± 2.4 yrs) were tested using a specially designed torque velocity device (TVD). This TVD is a hardware interface with the subject's lower leg which stabilizes the leg for calf muscle strength measurements. Calf muscle strength measurements consisted of 1) isometric force production at ankle angles of 80, 90, and 100 degrees of plantar flexion, 2) peak torque at six isokinetic angular velocities 0.52, 1.05, 2.09, 3.14, 4.19, and 5.24 rad × s^-1, and 3) a fatigue test consisting of 30 maximal contractions at 3.14 rad × s^-1. The greatest force production occurred at 80 degrees of ankle plantar flexion (148.5 ± 40.2 Nm). Isokinetic force production ranged from 114.1 ± 24.7 Nm at 0.52 rad × s^-1 to 16.8 ± 6.5 Nm at 5.24 rad × s^-1. A fatigue test consisting of 30 maximal repetitions at 3.14 rad × s^-1 resulted in a 61 ± 15 % decline in force production. To assess reproducibility and day to day variation, measurements at 1.05 and 2.09 rad × s^-1 were made during five different trials in a single day and one trial per day for three days, respectively. The within subject coefficient of variation was 2.6 to 6.5 % for reproducibility and 1.9 to 7.4 % for day to day variation. Magnetic resonance imaging (MRI) of the lower limb and muscle biopsy specimens from the gastrocnemius (lateral head) and soleus muscles were obtained to examine the relationship between strength and morphological characteristics of the calf muscles. Cross-sectional area of the primary plantar flexors (gastrocnemius and soleus) was 47.9 ± 1.3 cm² while muscle volume was 642 ± 16 cm³. Muscle fiber composition of the gastrocnemius and soleus averaged 57 ± 2 and 85 ± 3 % type I fibers, respectively. A poor correlation was found between fiber type and maximal isometric force production (r = 0.38; p > 0.05). However, calf muscle strength and muscle size was positively correlated (r = 0.76; p < 0.05). These data indicate that using the TVD interface to stabilize the lower leg is a reliable and reproducible procedure for the measurement of calf muscle strength.

Key words:

Muscle strength, exercise, contractile function, reproducibility.

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