Raw BIA variables (phase angle and impedance ratio) are significant predictors of handgrip strength in adolescents and young adults

Abstract Musculoskeletal fitness and body composition are major components of health-related physical fitness that are expected to be linked to each other. The aim of the study was to explore the association of musculoskeletal fitness (expressed as handgrip strength=HGS) with raw bioelectrical impedance analysis (BIA) variables and other predictors in the second and third decade of life. Four groups of healthy normal-weight and overweight subjects were studied: 130 male adolescents (age 16.0±1.1 years), 143 female adolescents (16.0±0.9 years), 141 young men (25.5±2.0 years) and 141 young women (25.2±1.9 years). Raw BIA variables (impedance=Z and phase angle=PhA) for the whole body were measured at five frequencies (5-50-100-250 kHz), while HGS was measured on both upper limbs. HGS was higher in males than females and in young men than male adolescents. A fairly strong correlation emerged in both genders between HGS and raw BIA variables, i.e. BI-indexes (stature²/Z), PhA and impedance ratios (IR=Z at high frequency/Z at low frequency). In multiple regression analysis, BI-index, PhA or IRs were more effective predictors of HGS than BIA-derived estimates of body composition or anthropometric variables such as stature, weight and body mass index. In both genders HGS was significantly higher in young adults than in adolescents for the same value of PhA or IR. In conclusion, this study provides some insight into the use of raw BIA variables and HGS in the first decades of life, suggesting a new approach for a reliable assessment of muscle quality in terms of both muscle structure and strength.