Reduced membrane cholesterol content in skeletal muscle is not essential for greater insulin-stimulated glucose uptake after acute exercise by rats

Phase angle, muscle tissue, and resistance training

The biophysical response of the human body to electric current is widely appreciated as a barometer of fluid distribution and cell function. From distinct raw bioelectrical impedance (BIA) variables assessed in the field of body composition, phase angle (PhA) has been repeatedly indicated as a functional marker of the cell's health and mass. Although resistance training (RT) programs have demonstrated to be effective to improve PhA, with varying degrees of change depending on other raw BIA variables, there is still limited research explaining the biological mechanisms behind these changes. Here, we aim to provide the rationale for the responsiveness of PhA determinants to RT, as well as to summarize all available evidence addressing the effect of varied RT programs on PhA of different age groups. Available data led us to conclude that RT modulates the cell volume by increasing the levels of intracellular glycogen and water, thus triggering structural and functional changes in different cell organelles. These alterations lead, respectively, to shifts in the resistive path of the electric current (resistance, R) and capacitive properties of the human body (reactance, Xc), which ultimately impact PhA, considering that it is the angular transformation of the ratio between Xc and R. Evidence drawn from experimental research suggests that RT is highly effective for enhancing PhA, especially when adopting high-intensity, volume, and duration RT programs combining other types of exercise. Still, additional research exploring the effects of RT on whole-body and regional BIA variables of alternative population groups is recommended for further knowledge development.

Exercise effects on γ3-AMPK activity, Akt substrate of 160 kDa phosphorylation, and glucose uptake in muscle of normal and insulin-resistant female rats

Previous studies demonstrated that acute exercise can enhance glucose uptake (GU), γ3-AMP-activated protein kinase (AMPK) activity, and Akt substrate of 160 kDa (AS160) phosphorylation in skeletal muscles from low-fat diet (LFD)- and high-fat diet (HFD)-fed male rats. Because little is known about exercise effects on these outcomes in females, we assessed postexercise GU by muscles incubated ± insulin, delta-insulin GU (GU of muscles incubated with insulin minus GU uptake of paired muscles incubated without insulin), and muscle signaling proteins from female rats fed a LFD or a brief HFD (2 wk). Rats were sedentary (LFD-SED, HFD-SED) or swim exercised. Immediately postexercise (IPEX) or 3 h postexercise (3hPEX), epitrochlearis muscles were incubated (no insulin IPEX; ±insulin 3hPEX) to determine GU. Muscle γ3-AMPK activity (IPEX, 3hPEX) and phosphorylated AS160 (pAS160; 3hPEX) were also assessed. γ3-AMPK activity and insulin-independent GU of IPEX rats exceeded sedentary rats without diet-related differences in either outcome. At 3hPEX, both GU by insulin-stimulated muscles and delta-insulin GU exceeded their respective diet-matched sedentary controls. GU by insulin-stimulated muscles, but not delta-insulin GU for LFD-3hPEX, exceeded HFD-3hPEX. LFD-3hPEX versus LFD-SED had greater γ3-AMPK activity and greater pAS160. HFD-3hPEX exceeded HFD-SED for pAS160 but not for γ3-AMPK activity. pAS160 and γ3-AMPK at 3hPEX did not differ between diet groups. These results revealed that increased γ3-AMPK activity at 3hPEX was not essential for greater GU in insulin-stimulated muscle or greater delta-insulin GU in HFD female rats. Similarly elevated γ3-AMPK activity in LFD-IPEX versus HFD-IPEX and pAS160 in LFD-3hPEX versus HFD-3hPEX may contribute to the comparable delta-insulin GU at 3hPEX in both diet groups.NEW & NOTEWORTHY Glucose uptake (GU) and phosphorylated AS160 (pAS160) by insulin-stimulated muscles at 3 h postexercise (3hPEX) exceeded diet-matched controls in female low-fat diet-fed (LFD) or high-fat diet-fed (HFD) rats. GU with insulin for LFD-3hPEX exceeded HFD-3hPEX, whereas pAS160 was similar between these groups. γ3-AMPK immediately postexercise (IPEX) was similarly elevated in LFD and HFD, but only LFD-3hPEX had increased γ3-AMPK. These results suggest that greater γ3-AMPK at IPEX and pAS160 at 3hPEX may contribute to elevated GU with insulin, but greater γ3-AMPK at 3hPEX was dispensable for female HFD rats.