Volume of ankle dorsiflexors and plantar flexors determined with stereological techniques

The validity of the methods used for determination of muscle mass has not b een evaluated previously. We determined muscle mass by estimating muscle vo lume with assumption-free stereological techniques applied to magnetic reso nance imaging (MRI) in 18 healthy untrained subjects (6 women, 12 men) aged 41 yr (29-64 yr; median, range). Muscle mass was also estimated by measuri ng leg circumference and cross-sectional muscle areas (CSA) from MRIs at th ree predetermined levels. Power [peak torque (PT)] of the ankle dorsiflexor s and plantar flexors was estimated by using isokinetic dynamometry. Dorsif lexor volume (r(2) = 0.76, P < 5 x 10(-6)) and CSA (r(2) = 0.73, P < 5 x 10 (-5)) were related to PT, whereas circumference was not (r(2) = 0.17, not s ignificant). Correspondingly, a relationship to plantar PT was established for plantar flexor volume (r(2) = 0.69, P < 5 x 10-5) and CSA (r(2) = 0.46, P < 5 x 10(-3)) but not leg circumference (r(2) = 0.15, not significant). SDs of the residuals were smaller for the relationship between dorsiflexor PT and volume than between PT and CSA (0.42 vs. 0.45) for plantar flexors ( 1.5 vs. 2.0). By using the Cavalieri method, six MRI sections and 15 min of point counting are sufficient to obtain a valid estimate of the volume of the muscles of the lower leg.