Regional Phase Angle As An Indicator Of Upper And Lower Body Strength Performance In Youth

It is not yet known whether regional bioelectrical impedance analysis (BIA) phase angle (PhA) may be informative of youths’ unilateral strength of upper and lower limbs, regardless of lean soft tissue mass (LSTM). PURPOSE: To examine the relevance of regional PhA in explaining unilateral upper and lower body strength performance of healthy youth. METHODS: A total of 634 participants (13.4 ± 2.1 years; 314 girls) were included in the present investigation. Regional raw BIA variables were determined using a phase-sensitive BIA device and LSTM was evaluated by dual-energy X-ray absorptiometry. Unilateral upper and lower body strength was assessed using the handgrip strength test (HGS) and both single-leg (SL) broad jump and SL vertical countermovement jump (CMJ). Multiple regression analysis models included sex, age, body mass index, and regional LSTM as covariates (M1: unadjusted; M2: all variables except LSTM; M3: fully adjusted model). RESULTS: Dominant and non-dominant arms’ PhA was positively associated with HGS (M1: β = 0.646 and β = 0.650; M2: β = 0.344 and β = 0.363, p < 0.001). When further adjusting for regional LSTM, the PhA of both arms remained positively associated with HGS (β = 0.105 and β = 0.139, p < 0.001). Regarding the lower limb strength, an association of regional PhA was found for both legs in the SL broad jump (M1: β = 0.369 and β = 0.331; M2: β = 0.315 and β = 0.282) and SL vertical CMJ (M1: β = 0.612 and β = 0.601; M2: β = 0.271 and β = 0.253, p < 0.001). After accounting for regional LSTM, the PhA of both legs continued to explain the strength resulting from the SL broad jump (β = 0.187 to 0.212) and SL vertical CMJ (β = 0.115 to 0.140; p < 0.001). CONCLUSIONS: Regional PhA may have the potential to be used as a marker of upper and lower body strength, which is important when it comes to assessing strength performance in youth. This is especially relevant because regional PhA appears to have its own biophysical characteristics to explain regional strength independently of LSTM. Fundação para a Ciência e Tecnologia [2020.07856.BD; SFRH/BD/149394/2019; UIDB/00447/2020]