Investigation of Skeletal Muscle Indices Affecting Anaerobic Thresholds after Acute Myocardial Infarction

To investigate skeletal muscle indices influencing the anaerobic threshold (AT) measured by cardiopulmonary exercise testing (CPX).

This study included 125 consecutive men (median age: 66.0 years) diagnosed with acute myocardial infarction who underwent CPX before discharge. Participants were categorized into two groups based on their AT: the AT-lowering and AT-maintaining groups, comprising those with AT <11 and ≥11 ml/min/kg, respectively. Skeletal muscle indices that influenced AT, strengths of such influences, and respective cutoff values were investigated using multiple logistic regression analysis, decision-tree analysis, and the random-forest method. Skeletal muscle indices included grip strength, knee extension strength, lower-limb skeletal muscle index, phase angle (PhA), lower-limb PhA, arm circumference (AC), and calf circumference.

Lower-limb PhA, AC, age, and body mass index (BMI) influenced AT (model X² test: p <0.05; Hosmer-Lemeshow test: p = 0.98). Among the skeletal muscle indices, Gini impurity reduction was the highest in the lower-limb PhA. The cutoff values for AT were ≥4.0° for BMI <24 kg/m² and ≥6.4° for BMI ≥24 kg/m².

Lower-limb PhA was the most influential skeletal muscle index affecting AT. PhA measured using body composition analyzers is useful to identify exercise-limiting factors and determine the effectiveness of exercise because it can be easily performed shortly.