Effects of aerobic morning intervention on body composition changes in young women of morning and neither chronotypes

This study aimed to compare the effect of a morning physical intervention on the body composition of young women (n = 8, mean age ± SD = 23.1 ± 1.0 years, mean height ± SD = 168.9 ± 5.8 cm, mean weight ± SD = 66.2 ± 6.8 kg) of the morning chronotype (M-types) vs. young women (n = 25, mean age ± SD = 21.4 ± 1.5 years, mean height ± SD = 167.1 ± 5.4 cm, mean weight ± SD = 65.6 ± 7.8 kg) of the neither chronotypes (N-types). We used bioimpedance analysis to detect changes in the following indicators: weight, body mass index, fat mass (FM%), fat free mass (FFM), muscle mass (MM), total body water (TBW), extracellular and total body water ratio (ECW/TBW), extracellular and body cell mass ratio (ECM/BCM), and phase angle (PA). Intervention effects in groups were compared and evaluated by Cohen’s d within the statistical procedure of paired samples t-test, which did not show any significant differences in all indicators, except PA, between the pre-test and post-test (p>0.05). Statistical improvement was denoted and examined in the PA of the N-types. The most significant difference was found in the ECM/BCM indicator, which was stimulated more effectively in M-types after the morning intervention compared with the N-types. M-type participants improved in ECM/BCM (d = 0.62) and PA (d = 0.70) with a medium effect, but scored worse in FM% (d = 0.47) with a small effect, FFM (d = .43), MM (d = 0.42), and TBW (d = 0.40), whereas no effect was found in ECW/TBW (d = 0.15). N-type participants improved in PA (d = .60) with a medium effect, FFM (d = 0.29), MM (d = 0.28), and ECW/TBW (d = 0.28) with a small effect; no effect was observed in ECM/BCM (d = 0.01), FM% (d = 0.03), and TBW (d = 0.04). The results showed that the ECM/BCM and PA parameters were more sensitive than the other parameters. Our findings indicate the importance of further exploration and examination of the problem of time effect examination on particular chronotypes.