Evaluation of the strength-size relationship in vivo using various muscle size indices

Purpose: It is well accepted that maximum strength is related to muscle siz e. The primary purpose of this study was to determine whether anthropometri c or dual-energy x-ray absorptiometry (DEXA) estimates of muscle size were valid predictors of plantar flexor maximum voluntary contraction (MVC) stre ngth and could be used in lieu of more sophisticated techniques (e.g., magn etic resonance imaging (MRI)). Additionally, we compared the relationship a mong MVC and three MRI-determined muscle size measures; anatomical (ACSA) a nd physiological (PCSA) cross-sectional areas; and muscle volume (VOLm). Me thods: We measured plantar flexor MVC at 1.83 rad and various indices of mu scle size: 1) body weight, 2) total body lean mass (LM) (DEXA), 3) lower le g LM (DEXA). 4) lower leg circumference, 5) estimated muscle+bone cross-sec tional area (CSA) from circumference and calf skin-fold, 6) triceps surae A CSA, 7) triceps surae PCSA, and (8) triceps surae volume (VOLm), in 39 prem enopausal women (mean +/- SD: 36 +/- 8 yr, 165 +/- 6 cm, and 65 +/- 9 kg). Results: Zero-order correlations showed significant (P < 0.05) associations between MVC and total body LM (r = 0.365), lower leg LM (r = 0.381), circu mference (r = 0.584), estimated muscle+bone CSA (r = 0.447), ACSA (r = 0.73 3), PCSA (r = 0.715), and VOL, (r = 0.649). By using the Fisher Z-transform ation, ACSA and PCSA correlated significantly higher with MVC (P < 0.05) th an anthropometric and DEXA indices. Further, only ACSA and PCSA regressed t o the origin, indicating the ability to predict MVC was greatest with these two measures. Conclusions: The MRI-determined muscle size indices, which w ere specific to the triceps surae, correlated with strength better than who le limb anthropometric and DEXA indices. In this group of women, both ACSA and PCSA appeared superior to VOLm for predicting strength. PCSA was not fo und to be more precise than ACSA. ACSA appears to provide adequate precisio n for estimating plantar flexor specific tension in vivo.