Limb-specific isometric and isokinetic strength in adults: The potential role of regional bioelectrical impedance analysis-derived phase angle

Abstract

Background & AimsIt is not yet known whether regional bioelectrical impedance (BIA) phase angle (PhA) may be informative of different types of strength performed by the lower and upper limbs, independently of lean soft tissue mass (LSTM). Using a sample of healthy adults, we aimed to examine the association and relevance of regional PhA relative to isometric and isokinetic strength of each limb. MethodsA total of 57 participants (32.7±12.9 years; 24.7±3.5 kg/m2) were included in the present investigation. Regional raw BIA variables were determined using a phase-sensitive BIA device. Dual-energy X-ray absorptiometry was used to evaluate LSTM. Absolute isometric and isokinetic (i.e., 60º/s and 180º/s) strength of each limb (extension and flexion) was assessed using an isokinetic dynamometer and used to calculate relative strength. ResultsIn absolute strength, only dominant leg PhA was associated with isometric extension strength (β=0.283) and isokinetic 180º/s flexion strength (β=0.354), regardless of LSTM (p<0.05). In relative strength, a significant association of regional PhA was found for dominant arm flexion isometric strength (β=0.336), and non-dominant arm and dominant leg extension isometric strength (β=0.377, β=0.565, respectively; p<0.05), independently of LSTM. Similarly, for isokinetic 180º/s strength, regional PhA significantly explained the variance in the relative strength of both arms and dominant leg (β=0.350 to 0.506), regardless of LSTM (p<0.05). Relative isokinetic 60º/s strength was not consistently associated with regional PhA (p≥0.05). ConclusionsRegional PhA significantly explained relative (isometric and 180º/s isokinetic strength of both arms and dominant leg), but not absolute muscle strength, independently of regional LSTM. Thus, after accounting for body size, regional PhA seems to have its own characteristics that explain relative strength independently of LSTM.