This study attempted to determine the relationship between creatine (Cr) accumulation in human skeletal muscle and erythrocytes following Cr supplementation. If a strong relationship exists, a blood test might provide a practical, less invasive alternative than muscle biopsy for evaluating cellular Cr accumulation. Eighteen active, but not well-trained males were supplemented with Cr (4 × 5g/d) for 5 d. Muscle biopsies (vastus lateralis) were obtained pre- and post-loading and analyzed for Cr, phosphocreatine (PCr), and total Cr (TCr) content. Venous blood was also drawn at these times to determine erythrocyte Cr concentrations. Muscle Cr, PCr, and TCr concentrations were elevated (P < 0.05) by 39.8%, 7.5%, and 20.1% respectively following supplementation. Erythrocyte Cr concentrations were also elevated (P < 0.01) following the loading period, although to a greater relative degree than tissue concentrations (129.6%). Pre- and post-loading erythrocyte Cr concentrations were poorly and nonsignificantly correlated with that observed in skeletal muscle. Further, loading-mediated increases in erythrocyte Cr concentrations were poorly correlated with elevations in muscle Cr (r = 0.07), PCr (r = 0.06) or TCr (r = 0.04) concentrations. Erythrocyte Cr concentrations can be augmented by 5 d of Cr supplementation, however, this elevation does not reflect that observed in skeletal muscle obtained by muscle biopsy. Consequently, erythrocyte response to Cr loading is not a reliable measure of skeletal muscle Cr/TCr accumulation.
David B. Preen, Brian T. Dawson, Carmel Goodman, John Beilby and Simon Ching
James Fell and Andrew Dafydd Williams
Recovery from exercise is integral to the physical training process. There is a perception among older athletes that aging negatively affects the recovery process. Plausible arguments for an impaired recovery with aging are a greater susceptibility of older muscle to exercise-induced skeletal-muscle damage and a slower repair and adaptation response. Differences in the physical activity level of the research participants are rarely considered, however. This makes it difficult to differentiate the respective roles of declining physical activity and aging on the recovery process. Furthermore, the type of exercise used to induce damage and monitor recovery is often not indicative of a normal training stimulus for athletes. This review discusses the effects of aging on skeletal-muscle damage and recovery processes and highlights the limitations of many of these studies with respect to older athletes. Future research should use an exercise intervention representative of a normal training stimulus and take the physical activity level of the participants into account.
Paul T. Reidy, Adam R. Konopka, J. Matthew Hinkley, Miranda K. Suer and Matthew P. Harber
We previously reported an increase in skeletal muscle protein synthesis during fasted and fed recovery from nonexhaustive aerobic exercise (Harber et al., 2010). The current study examined skeletal muscle intracellular signaling in the same subjects to further investigate mechanisms of skeletal muscle protein metabolism with and without feeding following aerobic exercise. Eight males (VO2peak: 52 ± 2 ml−1.kg−1.min−1) performed 60-min of cycle ergometry at 72 ± 1% VO2peak on two occasions in a counter-balanced design. Exercise trials differed only in the postexercise nutritional intervention: EX-FED (5kcal, 0.83g carbohydrate, 0.37g protein, 0.03g fat per kg body weight) and EX-FAST (noncaloric, isovolumic placebo) ingested immediately and one hour after exercise. Muscle biopsies were obtained from the vastus lateralis at rest (on a separate day) and two hours postexercise to assess intracellular signaling via western blotting of p70S6K1, eEF2, 4EBP1, AMPKα and p38 MAPK. p70S6K1 phosphorylation was elevated (p < .05) in EX-FED relative to REST and EX-FAST. eEF2, 4EBP1, AMPKα and p38 MAPK signaling were unaltered at 2h after exercise independent of feeding status when expressed as the ratio of phosphorylated to total protein normalized to actin. These data demonstrate that feeding after a nonexhaustive bout of aerobic exercise stimulates skeletal muscle p70S6K1 intracellular signaling favorable for promoting protein synthesis which may, as recent literature has suggested, better prepare the muscle for subsequent exercise bouts. These data provide further support into the role of feeding on mechanisms regulating muscle protein metabolism during recovery from aerobic exercise.
Stephen M. Paridon, Steven B. Wolfe, Chau P. Lee, Michael A. Nigro and William W. Pinsky
To determine whether defects of skeletal muscle oxidative phosphorylation can be differentiated from other causes of skeletal muscle weakness by aerobic responses to exercise, 10 patients with oxidative phosphorylation abnormalities (n = 5) or defects of contractile element apparatus or peripheral neuropathy (n = 5) underwent bicycle exercise testing. Results were compared with 16 healthy control subjects. The response of oxygen consumption to work rate and ventilatory threshold were significantly reduced in the oxidative phosphorylation group when compared to subjects with other causes of muscle weakness and the control group. Exercise testing appears to be useful in distinguishing patients with defects of oxidative phosphorylation from those with other causes of skeletal muscle weakness.
Jon N. Swift Jr., James P. Kehrer, K. Stephen Seiler and Joseph W. Starnes
The purpose of this study was to determine whether submaximal exercise significantly changes the concentration of vitamin E (αToc) in rat liver and skeletal muscle and to establish a time course for the return to basal levels. Male Sprague-Dawley rats, age 8 to 10 weeks, were randomly divided into sedentary control (Con) (n = 7) and exercise n = 17) groups. Exercised animals ran 100 min on a motorized treadmill at approximately 70% VO2max for 3 consecutive days. They were then sacrificed immediately postexercise (0Post), 24 hr post (24Post), or 72 hr post (72Post). The gastrocnemius, red vastus lateralis (RV), white vastus lateralis (WV), and liver were excised and analyzed for αToc concentration by high-performance liquid chromolography utilizing electrochemical detection. We found that after 3 consecutive days of exercise, αToc was reduced in RV and WV at 0Post and 24Post but returned to control values by 72Post. Liver αToc content was not changed at OPost but was significantly reduced at 24 Post and 72 Post. No significant changes in αToc were observed in the gastrocnemius in response to exercise. The data indicate that following an exercise-related decrease, skeletal muscle vitamin E concentration requires more than 24 hr to return to the preexercise concentration, and that the replenishment process may involve redistribution of vitamin E from liver to muscle.
David Preen, Brian Dawson, Carmel Goodman, John Beilby and Simon Ching
The purposes of this investigation were first to determine the impact of 3 different creatine (Cr) loading procedures on skeletal muscle total Cr (TCr) accumulation and, second, to evaluate the effectiveness of 2 maintenance regimes on retaining intramuscular TCr stores, in the 6 weeks following a 5-day Cr loading program (20 g · day−1). Eighteen physically active male subjects were divided into 3 equal groups and administered either: (a) Cr (4 X 5 g · day−1 X 5 days), (b) Glucose+Cr (1 g · kg−1 of body mass twice per day), or (c) Cr in conjunction with 60 min of daily muscular (repeated-sprint) exercise. Following the 5-day loading period, subjects were reassigned to 3 maintenance groups and ingested either 0 g · day−1, 2 g · day−1 or 5 g · day−1 of Cr for a period of 6 weeks. Muscle biopsy samples (vastus lateralis) were taken pre- and post-loading as well as post-maintenance and analyzed for skeletal muscle ATP, phosphocreatine (PCr), Cr, and TCr concentrations. Twenty-four hour urine samples were collected for each of the loading days and last 2 maintenance days, and used to determine whole body Cr retention. Post-loading TCr stores were significantly (p < .05) increased in all treatment conditions. The Glucose+Cr condition produced a greater elevation (p < .05) in TCr concentrations (25%) than the Cr Only (16%) or Exercise+Cr (18%) groups. Following the maintenance period, muscle TCr stores were still similar to post-loading values for both the 2 g · day−1 and 5 g · day−1 conditions. Intramuscular TCr values for the 0 g · day−1 condition were significantly lower than the other conditions after the 6-week period. Although not significantly different from pre-loading concentrations, muscle TCr for the 0 g · day−1 group had not fully returned to baseline levels at 6 weeks post-loading. The data suggests that Glucose+Cr (but with a much smaller glucose intake than currently accepted) is potentially the most effective means of elevating TCr accumulation in human skeletal muscle. Furthermore, after 5 days of Cr loading, elevated muscle TCr concentrations can be maintained by the ingestion of small daily Cr doses (2-5 g) for a period of 6 weeks and that TCr concentrations may take longer than currently accepted to return to baseline values after such a Cr loading regime.
Élvio R. Gouveia, Bruna R. Gouveia, José A. Maia, Cameron. J. Blimkie and Duarte L. Freitas
The aims of this study were to describe age- and sex-related differences in total body skeletal muscle (TB-SM) mass and to determine the variance explained by physical activity (PA). This cross-sectional study included 401 males and 402 females, aged 60–79 years. TB-SM was determined by dual-energy x-ray absorptiometry (DXA) and PA by Baecke questionnaire. Statistical analysis included t test, ANOVAs, Pearson correlations, and multiple regression analysis. TB-SM mass was higher in the youngest age group when compared with the oldest in males and females. Males had greater TB-SM values than females. PA made a significant and positive contribution to the variation in TB-SM, β = 0.071; p = .016. Sex, height, fat mass, and PA explained 77% of the variance in TB-SM. The oldest cohorts and females had lower TB-SM than the younger cohorts and males. This study suggests that PA exerts a significant role in the explanation of TB-SM.
Leonard S. Jefferson and Scot R. Kimball
Gain or loss of skeletal muscle mass is due largely to the establishment of an imbalance between rates of protein synthesis and degradation. A key determinant of the rate of protein synthesis is translation initiation, a process regulated in part through binding of initiator methionyl-tRNA (met-tRNAi) and messenger RNA (mRNA) to a 40S ribosomal subunit. Either the met-tRNAi or mRNA binding step can become limiting for protein synthesis. Furthermore, the mRNA binding step can modulate translation of specific mRNAs with or without changes in the overall rate of protein synthesis. This report highlights molecular mechanisms involved in mediating control of the mRNA binding step in translation initiation. Particular attention is given to the effect of exercise on this step and to how the branched-chain amino acid leucine stimulates muscle protein synthesis after exercise. Potential mechanisms for exercise induced increase in muscle mass are discussed.
Heather M. Logan-Sprenger, George J. F. Heigenhauser, Graham L. Jones and Lawrence L. Spriet
This study investigated the effects of progressive mild dehydration during cycling on whole-body substrate oxidation and skeletal-muscle metabolism in recreationally active men. Subjects (N = 9) cycled for 120 min at ~65% peak oxygen uptake (VO2peak 22.7 °C, 32% relative humidity) with water to replace sweat losses (HYD) or without fluid (DEH). Blood samples were taken at rest and every 20 min, and muscle biopsies were taken at rest and at 40, 80, and 120 min of exercise. Subjects lost 0.8%, 1.8%, and 2.7% body mass (BM) after 40, 80, and 120 min of cycling in the DEH trial while sweat loss was not significantly different between trials. Heart rate was greater in the DEH trial from 60 to 120 min, and core temperature was greater from 75 to 120 min. Rating of perceived exertion was higher in the DEH trial from 30 to 120 min. There were no differences in VO2, respiratory-exchange ratio, total carbohydrate (CHO) oxidation (HYD 312 ± 9 vs. DEH 307 ± 10 g), or sweat rate between trials. Blood lactate was significantly greater in the DEH trial from 20 to 120 min with no difference in plasma free fatty acids or epinephrine. Glycogenolysis was significantly greater (24%) over the entire DEH vs. HYD trial (433 ± 44 vs. 349 ± 27 mmol · kg−1 · dm−1). In conclusion, dehydration of <2% BM elevated physiological parameters and perceived exertion, as well as muscle glycogenolysis, during exercise without affecting whole-body CHO oxidation.
Resistance exercise can effectively result in an increase in muscle mass, or hypertrophy, which generally becomes apparent after several weeks of training. Muscle hypertrophy requires muscle protein synthesis to exceed protein breakdown during an extended time period. It has been firmly established that the interaction between exercise and nutrition (i.e., protein intake) is necessary to attain net protein accretion in skeletal muscle. The stimulation of protein synthesis is caused in part by stimulation of mRNA translation initiation. There is relatively little information on the response of intracellular signaling controlling mRNA translation to exercise and nutrition, especially in humans, but the available data in humans seem to suggest that a single bout of resistance exercise does not substantially enhance PI-3 kinase/mTOR signaling during the first 2 h after exercise. Moreover, it is demonstrated that the ingestion of protein or amino acids after exercise is crucial to further stimulate molecular signaling that controls translation initiation. The aim of this review is to provide an overview of the intracellular signaling related to translational control and to provide a summary of the current knowledge about the response of the signaling pathways controlling the anabolic response to exercise and nutrient intake in vivo in humans.