Relevance of body weight adaptation and modern obesity-defining parameters in the analysis of isokinetic trunk strength in people with obesity – A retrospective analysis

Pathologic values of body mass index (BMI), body weight, and waist circumference correlate with higher absolute and lower relative trunk strength. Whether waist-to-height ratio (WHtR) is appropriate for showing trunk strength differences in people with obesity and whether a continuous linear relationship exists between the increase in obesity and trunk strength is unknown. This retrospective cross-sectional study included 1174 subjects (1114 men and 60 women). Measured values included body weight, height, waist circumference, WHtR, BMI, and both absolute and body weight-adapted trunk flexor/extensor strength. Statistical analyses included t-tests, Welch tests, Pearson correlations, mixed-linear, and nonlinear regression analyses. Positive correlations with absolute trunk strength were found in subjects without obesity for all anthropometric parameters except WHtR. Weaker positive and partly negative correlation and linear regression coefficients were found in subjects with obesity. Nonlinear relationships were found between age, BMI, WHtR, and absolute respective body weight-adapted trunk strength. The relationship between obesity-defining measures/ indices and trunk strength is non-linear. Increasing BMI, waist circumference, or WHtR above cut-off values known from cardiovascular research is linked to a decrease or weaker increase in trunk strength. Body weight adaptation is recommended to avoid misinterpretation of apparently good absolute trunk strength values in people with obesity.