There is a growing body of evidence showing that the phase angle (PhA) can be used as an indicator of nutritional status, disease prognosis, and mortality risk. Still, it is unknown whether PhA can be used as a marker of muscular strength, maximal aerobic capacity, and skeletal muscle index (SMI) in obese former highly active individuals, an understudied population. This study aimed to analyze the association between PhA with SMI, maximal isometric strength, and maximal aerobic capacity (VO2max) in overweight/obese and inactive former athletes.
Cross-sectional data of 95 (63 males) former adult athletes (age: 43.1±9.4 yrs; BMI: 31.4±4.8 kg.m-2) participating in a weight loss clinical trial (clinicaltrials.gov: NCT03031951) was analyzed. Bioelectrical impedance (BI) spectroscopy was used to assess PhA at frequency 50. Total and regional fat and fat-free mass (FFM) were determined by dual-energy x-ray absorptiometry while skeletal muscle index was predicted from appendicular lean-soft tissue. Upper and lower-body maximal isometric strength was assessed by handgrip and leg press dynamometry. VO2max was determined by indirect calorimetry through a graded exercise test performed in a treadmill.
PhA was moderately associated with upper-body strength (r=0.556, p<0.001), lower-body strength (r=0.490, p<0.001), VO2max (r=0.328, p=0.013), and SMI (r=0.510, p<0.001). These relationships remained significant for maximal isometric strength (Upper-body: β=2.082, p=0.025; Lower-body: β=26.679, p=0.010) after adjusting for age, FFM, and sex but not for VO2max (β=1.175, p=0.323). SMI predicted PhA, after adjusting for sex and age (β=0.283, p=0.005).
Our findings indicated that former athletes with higher values of phase angle showed greater muscular isometric strength and SMI, regardless of sex, age and body composition, which suggests that this simple raw BI parameter can be used as a marker of muscularity and functionality in overweight/obese and inactive former athletes.