EMG-Normalised Kinase Activation during Exercise Is Higher in Human Gastrocnemius Compared to Soleus Muscle

In mice, certain proteins show a highly confined expression in specific muscle groups. Also, resting and exercise/contraction-induced phosphorylation responses are higher in rat skeletal muscle with low mitochondrial content compared to muscles with high mitochondrial content, possibly related to differential reactive oxygen species (ROS)-scavenging ability or resting glycogen content. To evaluate these parameters in humans, biopsies from soleus, gastrocnemius and vastus lateralis muscles were taken before and after a 45 min inclined (15%) walking exercise bout at 69% VO2max aimed at simultaneously activating soleus and gastrocnemius in a comparable dynamic work-pattern. Hexokinase II and GLUT4 were 46–59% and 26–38% higher (p<0.05) in soleus compared to the two other muscles. The type I muscle fiber percentage was highest in soleus and lowest in vastus lateralis. No differences were found in protein expression of signalling proteins (AMPK subunits, eEF2, ERK1/2, TBC1D1 and 4), mitochondrial markers (F1 ATPase and COX1) or ROS-handling enzymes (SOD2 and catalase). Gastrocnemius was less active than soleus measured as EMG signal and glycogen use yet gastrocnemius displayed larger increases than soleus in phosphorylation of AMPK Thr172, eEF2 Thr56 and ERK 1/2 Thr202/Tyr204 when normalised to the mean relative EMG-signal. In conclusion, proteins with muscle-group restricted expression in mice do not show this pattern in human lower extremity muscle groups. Nonetheless the phosphorylation-response is greater for a number of kinase signalling pathways in human gastrocnemius than soleus at a given activation-intensity. This may be due to the combined subtle effects of a higher type I muscle fiber content and higher training status in soleus compared to gastrocnemius muscle

Young, healthy males and females present cardiometabolic protection against the detrimental effects of a 7-day high-fat high-calorie diet

Purpose: High-fat, high-calorie (HFHC) diets have been used as a model to investigate lipid-induced insulin resistance. Short-term HFHC diets reduce insulin sensitivity in young healthy males, but to date, no study has directly compared males and females to elucidate sex-specific differences in the effects of a HFHC diet on functional metabolic and cardiovascular outcomes. Methods: Eleven males (24 ± 4 years; BMI 23 ± 2 kg.m−2; V̇O2 peak 62.3 ± 8.7 ml.min−1.kg−1FFM) were matched to 10 females (25 ± 4 years; BMI 23 ± 2 kg.m−2; V̇O2 peak 58.2 ± 8.2 ml.min−1.kg−1FFM). Insulin sensitivity, measured via oral glucose tolerance test, metabolic flexibility, arterial stiffness, body composition and blood lipids and liver enzymes were measured before and after 7 days of a high-fat (65% energy) high-calorie (+ 50% kcal) diet. Results: The HFHC diet did not change measures of insulin sensitivity, metabolic flexibility or arterial stiffness in either sex. There was a trend towards increased total body fat mass (kg) after the HFHC diet (+ 1.8% and + 2.3% for males and females, respectively; P = 0.056). In contrast to females, males had a significant increase in trunk to leg fat mass ratio (+ 5.1%; P = 0.005). Conclusion: Lean, healthy young males and females appear to be protected from the negative cardio-metabolic effects of a 7-day HFHC diet. Future research should use a prolonged positive energy balance achieved via increased energy intake and reduced energy expenditure to exacerbate negative metabolic and cardiovascular functional outcomes to determine whether sex-specific differences exist under more metabolically challenging conditions