Functional performance of lower limb muscles and contractile properties of chemically skinned single muscle fibers were evaluated before and after 8 wk of maximal effort stretch-shortening cycle (SSC) exercise training. Muscle biopsies were obtained from the vastus lateralis of eight men before and after the training period. Fibers were evaluated regarding their mechanical properties and subsequently classified according to their myosin heavy chain content (SDS-PAGE). After training, maximal leg extensor muscle force and vertical jump performance were improved 12% (P < 0.01) and 13% (P < 0.001), respectively. Single-fiber cross-sectional area increased 23% in type I (P < 0.01), 22% in type IIa (P < 0.001), and 30% in type IIa/IIx fibers (P < 0.001). Peak force increased 19% in type I (P < 0.01), 15% in type IIa (P < 0.001), and 16% in type IIa/IIx fibers (P < 0.001). When peak force was normalized with cross-sectional area, no changes were found for any fiber type. Maximal shortening velocity was increased 18, 29, and 22% in type I, IIa, and hybrid IIa/IIx fibers, respectively (P < 0.001). Peak power was enhanced in all fiber types, and normalized peak power improved 9% in type IIa fibers (P < 0.05). Fiber tension on passive stretch increased in IIa/IIx fibers only (P < 0.05). In conclusion, short-term SSC exercise training enhanced single-fiber contraction performance via force and contraction velocity in type I, IIa, and IIa/IIx fibers. These results suggest that SSC exercises are an effective training approach to improve fiber force, contraction velocity, and therefore power.

In humans, nutrient deprivation and extreme endurance exercise both activate autophagy. We hypothesized that cumulating fasting and cycling exercise would potentiate activation of autophagy in skelet...

Long-term oral creatine supplementation does not impair renal function in healthy athletes. Med. Sci. Sports Exerc., Vol. 31, No. 8, pp. 1108-1110, 1999. Oral creatine supplementation is widely used in sportsmen and women. Side effects have been postulated, but no thorough investigations have been conducted to support these assertions. It is important to know whether long-term oral creatine supplementation has any detrimental effects on kidney function in healthy population. Creatinine, urea, and plasma albumin clearances have been determined in oral creatine consumers (10 months to 5 yr) and in a control group. There were no statistical differences between the control group and the creatine consumer group for plasma contents and urine excretion rates for creatinine, urea, and albumin. Clearance of these compounds did not differ between the two groups. Thus, glomerular filtration rate, tubular reabsorption, and glomerular membrane permeability were normal in both groups. Neither short-term, medium-term, nor long-term oral creatine supplements induce detrimental effects on the kidney of healthy individuals.

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) originated in China in late 2019 and has since spread rapidly to every continent in the world. This pandemic continues to cause widespread personal suffering, along with severe pressure on medical and health care providers. The symptoms of SARS‐CoV‐2 and the subsequent prognosis are worsened in individuals who have preexisting comorbidities prior to infection by the virus. Individuals with obesity or overweight, insulin resistance, and diabetes typically have chronic low‐grade inflammation characterized by increased levels of several proinflammatory cytokines and the inflammasome; this state predisposes to greater risk for infection along with more adverse outcomes. Here, we consider whether a high level of cardiorespiratory fitness induced by prior exercise training may confer some innate immune protection against COVID‐19 by attenuating the “cytokine storm syndrome” often experienced by “at risk” individuals.

High-fat diets are known to decrease muscle protein synthesis, the adaptation to overload, and insulin sensitivity. Conditions that disrupt endoplasmic reticulum (ER) homeostasis lead to the activation of the unfolded protein response (UPR) that is associated with decreases in protein synthesis, chronic inflammation, and insulin resistance. The purpose of the present study was to establish whether ER stress is induced by a high-fat diet in skeletal muscle and whether ER stress can decrease mTORC1 activity and protein synthesis in muscle cells. Two independent protocols of high-fat feeding activated the UPR in mice. In the first study, mice consuming a high-fat diet containing 70% fat and <1% carbohydrates for 6 wk showed higher markers of the UPR (BiP, IRE1α, and MBTPS2) in the soleus and in the tibialis anterior muscles and ATF4 in the tibialis anterior ( P < 0.05). In the second study, a 20-wk high-fat diet containing 46% fat and 36% carbohydrates also increased BiP, IRE1α, and phospho-PERK protein and the expression of ATF4, CHOP, and both the spliced and unspliced forms of XBP1 in the plantar flexors ( P < 0.05). In C₂C₁₂muscle cells, tunicamycin, thapsigargin, and palmitic acid all increased UPR markers and decreased phosphorylation of S6K1 ( P < 0.05). Collectively, these data show that a high-fat diet activates the UPR in mouse skeletal muscle in vivo. In addition, in vitro studies indicate that palmitic acid, and other well-known ER stress inducers, triggered the UPR in myogenic cells and led to a decrease in protein synthesis and mTORC1 activity.