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Exercise elicits direct benefits to insulin sensitivity but may also indirectly improve glucose uptake by hemodynamic conditioning of the vasculature. The purpose of this study was to examine the modifying effect of 3 different types of exercise on the vascular response to an oral glucose challenge. Twenty healthy adults (9 women, 11 men; aged 23 ± 3 years) completed a standard oral glucose tolerance test (OGTT) at rest, as well as 1.5 hours after moderate continuous cycling exercise (30 min; 65% peak oxygen consumption), high-intensity interval cycling exercise (10 × 1 min at 90% peak heart rate), and lower-load higher-repetition resistance exercise (25–35 repetitions/set, 3 sets). Brachial and superficial femoral artery blood flow, conductance, and oscillatory shear index were measured throughout the OGTT. Regardless of rested state or exercise preconditioning, the OGTT induced reductions in brachial artery blood flow and conductance (p < 0.001), and transient increases in brachial and superficial femoral artery oscillatory shear index and retrograde blood flow (p < 0.01). Continuous cycling and resistance exercise were followed with a small degree of protection against prolonged periods of oscillatory flow. Our findings imply transient peripheral vasoconstriction and decreased limb blood flow during a standard OGTT, for which prior exercise was unable to prevent in healthy adults. Novelty: We investigated the impact of continuous, interval, and resistance exercise on the hemodynamic response to an OGTT. Our findings suggest decreased upper-limb blood flow during an OGTT is not prevented by prior exercise in healthy adults.

Proteins that coat the lipid droplets (also known as PAT proteins or perilipin (PLIN) family proteins) have diverse functions that are not well elucidated in many tissues. In skeletal muscle, there is even less known about the functions or characteristics of these proteins or how they might change in response to perturbations that alter both intramyocellular lipid (IMCL) content and fat utilization and oxidation. Therefore, the purpose of this study was to examine the human muscle content and gene expression of the four skeletal muscle PLIN proteins in both lean and obese men and women and how this was changed following a 12-week endurance training protocol. PLIN2–PLIN5 proteins were all more abundant in women than in men (p = 0.037 and p < 0.0001, respectively), consistent with higher IMCL content observed in female skeletal muscle. PLIN5 (previously known as OXPAT) is of particular interest because it has previously been associated primarily with oxidative tissues that rely heavily on fat oxidation for energy production. Although PLIN5 was not different between lean and obese subjects, it was the only PLIN protein to increase in response to endurance training in both sexes. PLIN5 correlated with IMCL volume (p < 0.0001), but in general, the other PLIN proteins did not correlate well with IMCL volume, suggesting that the relationship between lipid accumulation and PLIN family protein content is not a simple one. Although more work is necessary, it is clear that PLIN5 likely plays an important role in IMCL accumulation and oxidation, both of which increase with endurance training in human skeletal muscle.

Carbohydrate (CHO) and fat constitute the main fuels used during endurance exercise. The purpose of this thesis was to determine how sex, menstrual cycle phase, estrogen, obesity, and endurance training (ET) influence substrate metabolism. In study 1, men (n = 11) and women (n = 13) underwent primed constant infusion of [6,6-2H] glucose with muscle biopsies taken before and after a 90 min bike ride at 65% VO2 peak. Luteal-phase women had lower muscle glycogen utilization compared with follicular-phase women. Women had lower respiratory exchange ratio (RER) and plasma glucose utilization than men. In study 2, men (n = 17) and women (n = 19) had muscle biopsies taken before and after a 90 min bike ride at 65% VO2 peak. Women had greater intramyocellular lipid (IMCL) content and lower RER during exercise, with no effect of sex on net IMCL utilization. In study 3, Men (n = 11) were treated with 17-β-estradiol (E2, 2 mg·d–1, 8 d) and placebo and underwent primed constant infusion of [6,6–2H] glucose with muscle biopsies taken before and after a 90 min bike ride at 65% VO2 peak. E2 lowered RER and plasma glucose oxidation during exercise, with no effect on muscle glycogen utilization. In study 4, lean (n = 12) and obese (n = 11) women underwent 12 weeks of ET with muscle biopsies taken before and after training. Obese women were insulin resistant compared with lean women. ET increased oxidative capacity and β-oxidation capacity, as well as mitochondrial content. ET redistributed IMCL from the subsarcolemmal region to the intermyofibrillar region of the muscle fibre. These studies demonstrate that substrate metabolism is affected by many factors in health and disease and the ability to manipulate these factors is of importance to athletes wishing to improve performance, as well as to obese individuals attempting to normalize an altered metabolic state.