Two weeks of single-leg immobilization alters intramyocellular lipid storage characteristics in healthy, young women.

Muscle disuse rapidly induces insulin resistance (IR). Despite a relationship between intramyocellular lipid (IMCL) content and IR, during muscle-disuse IR develops before IMCL accumulation, suggesting that IMCL are not related to disuse-induced IR. However, recent studies show that it is not total IMCL content, but IMCL size and location that are related to IR. Changes in these IMCL parameters may occur prior to increases in IMCL content, thus contributing to disuse-induced IR. Omega-3 fatty acids may mitigate the effects of disuse on IR by preventing a decline in insulin signaling proteins. Twenty women (age 22 ± 3 yr) received either 5 g·day-1 omega-3 fatty acid or isoenergetic sunflower oil for 4 wk prior to, throughout 2 wk of single-leg immobilization, and during 2 wk of recovery. Changes in IMCL characteristics and insulin signaling proteins were examined in vastus lateralis samples taken before supplementation and immobilization, and following immobilization and recovery. Omega-3 supplementation had no effect. IMCL area density decreased in the subsarcolemmal region during immobilization and recovery (-19% and -56%, respectively, P = 0.009). IMCL size increased in the central intermyofibrillar region during immobilization (43%, P = 0.007), returning to baseline during recovery. PLIN5 and AKT increased during immobilization (87%, P = 0.002; 30%, P = 0.007, respectively). PLIN 5 remained elevated and AKT increased further (15%) during recovery. IRS1, AS160, and GLUT4 decreased during immobilization (-35%, P = 0.001; -44%, P = 0.03; -56%, P = 0.02, respectively), returning to baseline during recovery. Immobilization alters IMCL storage characteristics while negatively affecting unstimulated insulin signaling protein content in young women.NEW & NOTEWORTHY We report that the subcellular storage location of IMCL is altered by limb immobilization, highlighting the need to evaluate IMCL storage location when assessing the effects of disuse on IMCL content. We also found that AKT content increased during immobilization in our female population, contrary to studies in males finding that AKT decreases during disuse, highlighting that men and women may respond differently to disuse and the necessity to include women in all research.

Potato Protein Isolate Stimulates Muscle Protein Synthesis at Rest and with Resistance Exercise in Young Women.

Skeletal muscle myofibrillar protein synthesis (MPS) increases in response to protein feeding and to resistance exercise (RE), where each stimuli acts synergistically when combined. The efficacy of plant proteins such as potato protein (PP) isolate to stimulate MPS is unknown. We aimed to determine the effects of PP ingestion on daily MPS with and without RE in healthy women. In a single blind, parallel-group design, 24 young women (21 ± 3 years, n = 12/group) consumed a weight-maintaining baseline diet containing 0.8 g/kg/d of protein before being randomized to consume either 25 g of PP twice daily (1.6 g/kg/d total protein) or a control diet (CON) (0.8 g/kg/d total protein) for 2 wks. Unilateral RE (~30% of maximal strength to failure) was performed thrice weekly with the opposite limb serving as a non-exercised control (Rest). MPS was measured by deuterated water ingestion at baseline, following supplementation (Rest), and following supplementation + RE (Exercise). Ingestion of PP stimulated MPS by 0.14 ± 0.09 %/d at Rest, and by 0.32 ± 0.14 %/d in the Exercise limb. MPS was significantly elevated by 0.20 ± 0.11 %/d in the Exercise limb in CON (P = 0.008). Consuming PP to increase protein intake to levels twice the recommended dietary allowance for protein augmented rates of MPS. Performance of RE stimulated MPS regardless of protein intake. PP is a high-quality, plant-based protein supplement that augments MPS at rest and following RE in healthy young women.

Supplementation with dietary ω-3 mitigates immobilization-induced reductions in skeletal muscle mitochondrial respiration in young women.

Omega-3 (ω-3) supplementation attenuates immobilization-induced atrophy; however, the underlying mechanisms remain unclear. Since mitochondrial dysfunction and oxidative stress have been implicated in muscle atrophy, we examined whether ω-3 supplementation could mitigate disuse-mediated mitochondrial dysfunction. Healthy young women (age = 22 ± 3 yr) randomly received control (n = 9) or ω-3 supplementation (n = 11; 3 g eicosapentaenoic acid, 2 g docosahexaenoic acid) for 4 wk prior to and throughout 2 wk of single-limb immobilization. Biopsies were performed before and after 3 and 14 d of immobilization for the assessment of mitochondrial respiration, H2O2 emission, and markers of ADP transport/lipid metabolism. In controls, immobilization rapidly (3 d) reduced (∼20%) ADP-stimulated mitochondrial respiration without altering ADP sensitivity or the abundance of mitochondrial proteins. Extending immobilization to 14 d did not further reduce mitochondrial coupled respiration; however, unlike following 3 d, mitochondrial proteins were reduced ∼20%. In contrast, ω-3 supplementation prevented immobilization-induced reductions in mitochondrial content and respiration throughout the immobilization period. Regardless of dietary supplement, immobilization did not alter mitochondrial H2O2 emission in the presence or absence of ADP, markers of cellular redox state, mitochondrial lipid-supported respiration, or lipid-related metabolic proteins. These data highlight the rapidity of mitochondrial adaptations in response to muscle disuse, challenge the necessity for increased oxidative stress during inactivity, and establish that ω-3 supplementation preserves oxidative phosphorylation function and content during immobilization.-Miotto, P. M., McGlory, C., Bahniwal, R., Kamal, M., Phillips, S. M., Holloway, G. P. Supplementation with dietary ω-3 mitigates immobilization-induced reductions in skeletal muscle mitochondrial respiration in young women.

Omega-3 fatty acid supplementation attenuates skeletal muscle disuse atrophy during two weeks of unilateral leg immobilization in healthy young women.

Omega-3 (n-3) fatty acid supplementation enhances muscle protein synthesis and muscle size. Whether n-3 fatty acid supplementation attenuates human muscle disuse atrophy is unknown. We determined the influence of n-3 fatty acid supplementation on muscle size, mass, and integrated rates of myofibrillar protein synthesis (MyoPS) following 2 wk of muscle disuse and recovery in women. Twenty women (BMI = 23.0 ± 2.3 kg/m2, age = 22 ± 3 yr) underwent 2 wk of unilateral limb immobilization followed by 2 wk of return to normal activity. Starting 4 wk prior to immobilization, participants consumed either 5 g/d of n-3 fatty acid or an isoenergetic quantity of sunflower oil (control). Muscle size and mass were measured pre- and postimmobilization, and after recovery. Serial muscle biopsies were obtained to measure integrated (daily) MyoPS. Following immobilization, the decline in muscle volume was greater in the control group compared to the n-3 fatty acid group (14 vs. 8%, P < 0.05) and was not different from preimmobilization at recovery in the n-3 fatty acid group; however, it was still lower in the control group ( P < 0.05). Muscle mass was reduced in the control group only ( P < 0.05). MyoPS was higher in the n-3 group compared with the control group at all times ( P < 0.05). We conclude that n-3 fatty acid supplementation attenuates skeletal muscle disuse atrophy in young women, which may be mediated by higher rates of MyoPS.-McGlory, C., Gorissen, S. H. M., Kamal, M., Bahniwal, R., Hector, A. J., Baker, S. K., Chabowski, A., Phillips, S. M. Omega-3 fatty acid supplementation attenuates skeletal muscle disuse atrophy during two weeks of unilateral leg immobilization in healthy young women.