Muscle Na+-K+-ATPase activity and isoform adaptations to intense interval exercise and training in well-trained athletes.

The Na+ -K+ -ATPase enzyme is vital in skeletal muscle function. We investigated the effects of acute high-intensity interval exercise, before and following high-intensity training (HIT), on muscle Na+ -K+ -ATPase maximal activity, content, and isoform mRNA expression and protein abundance. Twelve endurance-trained athletes were tested at baseline, pretrain, and after 3 wk of HIT (posttrain), which comprised seven sessions of 8 x 5-min interval cycling at 80% peak power output. Vastus lateralis muscle was biopsied at rest (baseline) and both at rest and immediately postexercise during the first (pretrain) and seventh (posttrain) training sessions. Muscle was analyzed for Na+ -K+ -ATPase maximal activity (3-O-MFPase), content ([3H]ouabain binding), isoform mRNA expression (RT-PCR), and protein abundance (Western blotting). All baseline-to-pretrain measures were stable. Pretrain, acute exercise decreased 3-O-MFPase activity [12.7% (SD 5.1), P < 0.05], increased alpha1, alpha2, and alpha3 mRNA expression (1.4-, 2.8-, and 3.4-fold, respectively, P < 0.05) with unchanged beta-isoform mRNA or protein abundance of any isoform. In resting muscle, HIT increased (P < 0.05) 3-O-MFPase activity by 5.5% (SD 2.9), and alpha3 and beta3 mRNA expression by 3.0- and 0.5-fold, respectively, with unchanged Na+ -K+ -ATPase content or isoform protein abundance. Posttrain, the acute exercise induced decline in 3-O-MFPase activity and increase in alpha1 and alpha3 mRNA each persisted (P < 0.05); the postexercise 3-O-MFPase activity was also higher after HIT (P < 0.05). Thus HIT augmented Na+ -K+ -ATPase maximal activity despite unchanged total content and isoform protein abundance. Elevated Na+ -K+ -ATPase activity postexercise may contribute to reduced fatigue after training. The Na+ -K+ -ATPase mRNA response to interval exercise of increased alpha- but not beta-mRNA was largely preserved posttrain, suggesting a functional role of alpha mRNA upregulation.

Chronic intermittent hypoxia and incremental cycling exercise independently depress muscle in vitro maximal Na+-K+-ATPase activity in well-trained athletes.

Athletes commonly attempt to enhance performance by training in normoxia but sleeping in hypoxia [live high and train low (LHTL)]. However, chronic hypoxia reduces muscle Na(+)-K(+)-ATPase content, whereas fatiguing contractions reduce Na(+)-K(+)-ATPase activity, which each may impair performance. We examined whether LHTL and intense exercise would decrease muscle Na(+)-K(+)-ATPase activity and whether these effects would be additive and sufficient to impair performance or plasma K(+) regulation. Thirteen subjects were randomly assigned to two fitness-matched groups, LHTL (n = 6) or control (Con, n = 7). LHTL slept at simulated moderate altitude (3,000 m, inspired O(2) fraction = 15.48%) for 23 nights and lived and trained by day under normoxic conditions in Canberra (altitude approximately 600 m). Con lived, trained, and slept in normoxia. A standardized incremental exercise test was conducted before and after LHTL. A vastus lateralis muscle biopsy was taken at rest and after exercise, before and after LHTL or Con, and analyzed for maximal Na(+)-K(+)-ATPase activity [K(+)-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase)] and Na(+)-K(+)-ATPase content ([(3)H]ouabain binding sites). 3-O-MFPase activity was decreased by -2.9 +/- 2.6% in LHTL (P < 0.05) and was depressed immediately after exercise (P < 0.05) similarly in Con and LHTL (-13.0 +/- 3.2 and -11.8 +/- 1.5%, respectively). Plasma K(+) concentration during exercise was unchanged by LHTL; [(3)H]ouabain binding was unchanged with LHTL or exercise. Peak oxygen consumption was reduced in LHTL (P < 0.05) but not in Con, whereas exercise work was unchanged in either group. Thus LHTL had a minor effect on, and incremental exercise reduced, Na(+)-K(+)-ATPase activity. However, the small LHTL-induced depression of 3-O-MFPase activity was insufficient to adversely affect either K(+) regulation or total work performed.

Acute plasma volume expansion: effect on metabolism during submaximal exercise.

To examine the effect of acute plasma volume expansion (PVE) on substrate selection during exercise, seven untrained men cycled for 40 min at 72 +/- 2% peak oxygen uptake (VO(2 peak)) on two occasions. On one occasion, subjects had their plasma volume expanded by 12 +/- 2% via an intravenous infusion of the plasma substitute Haemaccel, whereas on the other occasion no such infusion took place. Muscle samples were obtained before and immediately after exercise. In addition, heart rate and pulmonary gas and venous blood samples were obtained throughout exercise. No differences in oxygen uptake or heart rate during exercise were observed between trials, whereas respiratory exchange ratio, blood glucose, and lactate were unaffected by PVE. Muscle glycogen and lactate concentrations were not different either before or after exercise. In addition, there was no difference in total carbohydrate oxidation between trials (control: 108 +/- 2 g; PVE group: 105 +/- 2 g). Plasma catecholamine levels were not affected by PVE. These data indicate that substrate metabolism during submaximal exercise in untrained men is unaltered by acute hypervolemia.

Preexercise carbohydrate ingestion, glucose kinetics, and muscle glycogen use: effect of the glycemic index.

Eight trained men cycled at 70% peak oxygen uptake for 120 min followed by a 30-min performance cycle after ingesting either a high-glycemic index (HGI), low-glycemic index (LGI), or placebo (Con) meal 30 min before exercise. Ingestion of HGI resulted in an elevated (P<0.01) blood glucose concentration compared with LGI and Con. At the onset of exercise, blood glucose fell (P<0.05) such that it was lower (P<0.05) in HGI compared with LGI and Con at 15 and 30 min during exercise. Plasma insulin concentration was higher (P<0.01) throughout the rest period after ingestion of HGI compared with LGI and Con. Plasma free fatty acid concentrations were lower (P<0.05) throughout exercise in HGI compared with LGI and Con. The rates of [6,6-(2)H]glucose appearance and disappearance were higher (P<0.05) at rest after ingestion and throughout exercise in HGI compared with LGI and Con. Carbohydrate oxidation was higher (P<0.05) throughout exercise, whereas glycogen use tended (P = 0.07) to be higher in HGI compared with LGI and Con. No differences were observed in work output during the performance cycle when comparing the three trials. These results demonstrate that preexercise carbohydrate feeding with a HGI, but not a LGI, meal augments carbohydrate utilization during exercise but does not effect exercise performance.

Effect of carbohydrate ingestion on metabolism during running and cycling.

The effects of carbohydrate or water ingestion on metabolism were investigated in seven male subjects during two running and two cycling trials lasting 60 min at individual lactate threshold using indirect calorimetry, U-14C-labeled tracer-derived measures of the rates of oxidation of plasma glucose, and direct determination of mixed muscle glycogen content from the vastus lateralis before and after exercise. Subjects ingested 8 ml/kg body mass of either a 6.4% carbohydrate-electrolyte solution (CHO) or water 10 min before exercise and an additional 2 ml/kg body mass of the same fluid after 20 and 40 min of exercise. Plasma glucose oxidation was greater with CHO than with water during both running (65 +/- 20 vs. 42 +/- 16 g/h; P < 0.01) and cycling (57 +/- 16 vs. 35 +/- 12 g/h; P < 0.01). Accordingly, the contribution from plasma glucose oxidation to total carbohydrate oxidation was greater during both running (33 +/- 4 vs. 23 +/- 3%; P < 0.01) and cycling (36 +/- 5 vs. 22 +/- 3%; P < 0.01) with CHO ingestion. However, muscle glycogen utilization was not reduced by the ingestion of CHO compared with water during either running (112 +/- 32 vs. 141 +/- 34 mmol/kg dry mass) or cycling (227 +/- 36 vs. 216 +/- 39 mmol/kg dry mass). We conclude that, compared with water, 1) the ingestion of carbohydrate during running and cycling enhanced the contribution of plasma glucose oxidation to total carbohydrate oxidation but 2) did not attenuate mixed muscle glycogen utilization during 1 h of continuous submaximal exercise at individual lactate threshold.

No effect of mild heat stress on the regulation of carbohydrate metabolism at the onset of exercise.

To investigate the influence of heat stress on the regulation of skeletal muscle carbohydrate metabolism, six active, but not specifically trained, men performed 5 min of cycling at a power output eliciting 70% maximal O2 uptake in either 20 degrees C (Con) or 40 degrees C (Heat) after 20 min of passive exposure to either environmental condition. Although muscle temperature (T(mu)) was similar at rest when comparing trials, 20 min of passive exposure and 5 min of exercise increased (P < 0.05) T(mu) in Heat compared with Con (37.5 +/- 0.1 vs. 36.9 +/- 0.1 degrees C at 5 min for Heat and Con, respectively). Rectal temperature and plasma epinephrine were not different at rest, preexercise, or 5 min of exercise between trials. Although intramuscular glycogen phosphorylase and pyruvate dehydrogenase activity increased (P < 0.05) at the onset of exercise, there were no differences in the activities of these regulatory enzymes when comparing Heat with Con. Accordingly, glycogen use in the first 5 min of exercise was not different when comparing Heat with Con. Similarly, no differences in intramuscular concentrations of glucose 6-phosphate, lactate, pyruvate, acetyl-CoA, creatine, phosphocreatine, or ATP were observed at any time point when comparing Heat with Con. These results demonstrate that, whereas mild heat stress results in a small difference in contracting T(mu), it does not alter the activities of the key regulatory enzymes for carbohydrate metabolism or glycogen use at the onset of exercise, when plasma epinephrine levels are unaltered.

Effect of acute plasma volume expansion on thermoregulation and exercise performance in the heat.

PURPOSE: We investigated the effects of acute plasma volume expansion on exercise performance in the heat. METHODS: Six moderately trained men cycled for 40 min at 64 +/- 2% peak pulmonary oxygen uptake (VO2peak) followed by an individual performance time trial, where subjects completed a set amount of work (267 +/- 15 kJ) in as little time as possible. Exercise trials were performed at 35 degrees C with a relative humidity of 40%. Subjects performed two exercise trials: one after 13.1 +/- 1% acute plasma volume expansion (PVE), which was achieved by the intravenous infusion of 8 mL x kg(-1) body weight of Hemaccel (35 g x L(-1) polygeline, 145 mmol x L(-1) Na+, and 145 mmol x L(-1) Cl-) and the other without prior treatment (CON). RESULTS: Core temperature, skin blood flow, and heart rate progressively increased (P < 0.05) during exercise, but no differences were observed between trials. Plasma glucose and lactate were similar at rest and during exercise, as was VO2 during exercise. Exercise performance was not influenced by plasma volume expansion (CON 17.5 +/- 0.4 min and PVE 17.1 +/- 0.2 min). CONCLUSION: These data suggest that, in moderately trained men, plasma volume expansion alone does not enhance thermoregulatory function and exercise performance during moderate intensity exercise in the heat.

Vitamin D status and musculoskeletal health in adolescent male ballet dancers a pilot study.

Adequate vitamin D levels during growth are critical to ensuring optimal bone development. Vitamin D synthesis requires sun exposure; thus, athletes engaged in indoor activities such as ballet dancing may be at relatively high risk of vitamin D insufficiency. The objective of this study was to investigate the prevalence of low vitamin D levels in young male ballet dancers and its impact on musculoskeletal health. Eighteen male ballet dancers, aged 10 to 19 years and training for at least 6 hours per week, were recruited from the Australian Ballet School, Melbourne, Australia. Serum 25(OH)D and intact PTH were measured in winter (July) from a non-fasting blood sample. Pubertal stage was determined using self-assessed Tanner criteria. Body composition and areal bone mineral density (aBMD) at the whole body and lumbar spine were measured using dual-energy x-ray absorptiometry (DXA). Injury history and physical activity levels were assessed by questionnaire. Blood samples were obtained from 16 participants. Serum 25(OH)D levels ranged from 20.8 to 94.3 nmol/L, with a group mean of 50.5 nmol/L. Two participants (12.5%) showed vitamin D deficiency [serum 25(OH)D level < 25 nmol/L], seven dancers (44%) had vitamin D insufficiency (25 to 50 nmol/L), and the remaining seven dancers (44%) had normal levels (> 50 nmol/L). No relationship was found between vitamin D status, PTH levels, body composition, and aBMD. The most commonly reported injuries were muscle tears and back pain. The average number of injuries reported by each dancer was 1.9 ± 0.4 (range: 0 to 5). There was no difference in the frequency of reported injuries between subjects with vitamin D deficiency or insufficiency (2.1 ± 0.6 injuries) and those with normal vitamin D levels (1.4 ± 0.6 injuries). This pilot study showed that more than half of highly-trained young male ballet dancers presented with low levels of vitamin D in winter. Further investigations in larger samples of adolescent athletes are needed to determine if this could negatively impact bone growth and place them at higher risk for musculoskeletal injuries.

Prolonged submaximal exercise induces isoform-specific Na+-K+-ATPase mRNA and protein responses in human skeletal muscle.

This study investigated effects of prolonged submaximal exercise on Na+-K+-ATPase mRNA and protein expression, maximal activity, and content in human skeletal muscle. We also investigated the effects on mRNA expression of the transcription initiator gene, RNA polymerase II (RNAP II), and key genes involved in protein translation, eukaryotic initiation factor-4E (eIF-4E) and 4E-binding protein 1 (4E-BP1). Eleven subjects (6 men, 5 women) cycled at 75.5% (SD 4.8%) peak O2 uptake and continued until fatigue. A vastus lateralis muscle biopsy was taken at rest, fatigue, and 3 and 24 h postexercise. We analyzed muscle for Na+-K+-ATPase alpha1, alpha2, alpha3, beta1, beta2, and beta3, as well for RNAP II, eIF-4E, and 4E-BP1 mRNA expression by real-time RT-PCR and Na+-K+-ATPase isoform protein abundance using immunoblotting. Muscle homogenate maximal Na+-K+-ATPase activity was determined by 3-O-methylfluorescein phosphatase activity and Na+-K+-ATPase content by [3H]ouabain binding. Cycling to fatigue [54.5 (SD 20.6) min] immediately increased alpha3 (P = 0.044) and beta2 mRNA (P = 0.042) by 2.2- and 1.9-fold, respectively, whereas alpha1 mRNA was elevated by 2.0-fold at 24 h postexercise (P = 0.036). A significant time main effect was found for alpha3 protein abundance (P = 0.046). Exercise transiently depressed maximal Na+-K+-ATPase activity (P = 0.004), but Na+-K+-ATPase content was unaltered throughout recovery. Exercise immediately increased RNAP II mRNA by 2.6-fold (P = 0.011) but had no effect on eIF-4E and 4E-BP1 mRNA. Thus a single bout of prolonged submaximal exercise induced isoform-specific Na+-K+-ATPase responses, increasing alpha1, alpha3, and beta2 mRNA but only alpha3 protein expression. Exercise also increased mRNA expression of RNAP II, a gene initiating transcription, but not of eIF-4E and 4E-BP1, key genes initiating protein translation.

Depressed Na+-K+-ATPase activity in skeletal muscle at fatigue is correlated with increased Na+-K+-ATPase mRNA expression following intense exercise.

We investigated whether depressed muscle Na(+)-K(+)-ATPase activity with exercise reflected a loss of Na(+)-K(+)-ATPase units, the time course of its recovery postexercise, and whether this depressed activity was related to increased Na(+)-K(+)-ATPase isoform gene expression. Fifteen subjects performed fatiguing, knee extensor exercise at approximately 40% maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue, 3 h, and 24 h postexercise and analyzed for maximal Na(+)-K(+)-ATPase activity via 3-O-methylfluorescein phosphatase (3-O-MFPase) activity, Na(+)-K(+)-ATPase content via [(3)H]ouabain binding sites, and Na(+)-K(+)-ATPase alpha(1)-, alpha(2)-, alpha(3)-, beta(1)-, beta(2)- and beta(3)-isoform mRNA expression by real-time RT-PCR. Exercise [352 (SD 267) s] did not affect [(3)H]ouabain binding sites but decreased 3-O-MFPase activity by 10.7 (SD 8)% (P < 0.05), which had recovered by 3 h postexercise, without further change at 24 h. Exercise elevated alpha(1)-isoform mRNA by 1.5-fold at fatigue (P < 0.05). This increase was inversely correlated with the percent change in 3-O-MFPase activity from rest to fatigue (%Delta3-O-MFPase(rest-fatigue)) (r = -0.60, P < 0.05). The average postexercise (fatigue, 3 h, 24 h) alpha(1)-isoform mRNA was increased 1.4-fold (P < 0.05) and approached a significant inverse correlation with %Delta3-O-MFPase(rest-fatigue) (r = -0.56, P = 0.08). Exercise elevated alpha(2)-isoform mRNA at fatigue 2.5-fold (P < 0.05), which was inversely correlated with %Delta3-O-MFPase(rest-fatigue) (r = -0.60, P = 0.05). The average postexercise alpha(2)-isoform mRNA was increased 2.2-fold (P < 0.05) and was inversely correlated with the %Delta3-O-MFPase(rest-fatigue) (r = -0.68, P < 0.05). Nonsignificant correlations were found between %Delta3-O-MFPase(rest-fatigue) and other isoforms. Thus acute exercise transiently decreased Na(+)-K(+)-ATPase activity, which was correlated with increased Na(+)-K(+)-ATPase gene expression. This suggests a possible signal-transduction role for depressed muscle Na(+)-K(+)-ATPase activity with exercise.

Are squash players protecting their eyes?

OBJECTIVE: To determine factors associated with adult squash players' protective eyewear behaviours. METHODS: A survey of 303 players (aged >or =18 years) was conducted at three squash venues in Melbourne, Australia over a three week period in June 2000 to obtain information about protective eyewear use. RESULTS: Of 303 participants the response rate was 98.1%; 66.1% were males, with a mean age of 40.5 years. The majority (68.4%) had played squash for 10 years or more. Although 18.8% of players reported using protective eyewear, only 8.9% reported wearing approved eyewear. Both age group (p<0.05) and years of squash experience (p<0.01) were significantly associated with any eyewear use. The two main influences were personal experience of eye injuries (50.0%) and knowledge of eye injury risk (33.9%). A commonly reported barrier was restriction of vision (34.2%). CONCLUSION: These findings demonstrate a low prevalence of voluntary use of appropriate protective eyewear. Future prevention strategies incorporating education campaigns should focus on increasing players' knowledge of risks. The barriers to use and misconceptions about which types of eyewear is most protective need to be addressed as a priority.

Effect of glycerol-induced hyperhydration on thermoregulation and metabolism during exercise in heat.

This study examined the effect of glycerol ingestion on fluid homeostasis, thermoregulation, and metabolism during rest and exercise. Six endurance-trained men ingested either 1 g glycerol in 20 ml H2O x kg(-1) body weight (bw) (GLY) or 20 ml H2O x kg(-1) bw (CON) in a randomized double-blind fashion, 120 min prior to undertaking 90 min of steady state cycle exercise (SS) at 98% of lactate threshold in dry heat (35 degrees C, 30% RH), with ingestion of CHO-electrolyte beverage (6% CHO) at 15-min intervals. A 15-min cycle, where performance was quantified in kJ, followed (PC). Pre-exercise urine volume was lower in GLY than CON (1119 +/- 97 vs. 1503 +/- 146 ml x 120 min(-1); p < .05). Heart rate was lower (p < .05) throughout SS in GLY, while forearm blood flow was higher (17.1 +/- 1.5 vs. 13.7 +/- 3.0 ml x 100 g tissue x min(-1); p < .05) and rectal temperature lower (38.7 +/- 0.1 vs. 39.1 +/- 0.1 degrees C; p < .05) in GLY late in SS. Despite these changes, skin and muscle temperatures and circulating catecholamines were not different between trials. Accordingly, no differences were observed in muscle glycogenolysis, lactate accumulation, adenine nucleotide, and phosphocreatine degradation or inosine 5'-monophosphate accumulation when comparing GLY with CON. Of note, the work performed during PC was 5% greater in GLY (252 +/- 10 vs. 240 +/- 9 kJ; p < .05). These results demonstrate that glycerol, when ingested with a bolus of water 2 hours prior to exercise, results in fluid retention, which is capable of reducing cardiovascular strain and enhancing thermoregulation. Furthermore, this practice increases exercise performance in the heat by mechanisms other than alterations in muscle metabolism.

Intense exercise up-regulates Na+,K+-ATPase isoform mRNA, but not protein expression in human skeletal muscle.

Characterization of expression of, and consequently also the acute exercise effects on, Na(+),K(+)-ATPase isoforms in human skeletal muscle remains incomplete and was therefore investigated. Fifteen healthy subjects (eight males, seven females) performed fatiguing, knee extensor exercise at approximately 40% of their maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue and 3 and 24 h postexercise, and analysed for Na(+),K(+)-ATPase alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) mRNA and crude homogenate protein expression, using Real-Time RT-PCR and immunoblotting, respectively. Each individual expressed gene transcripts and protein bands for each Na(+),K(+)-ATPase isoform. Each isoform was also expressed in a primary human skeletal muscle cell culture. Intense exercise (352 +/- 69 s; mean +/-s.e.m.) immediately increased alpha(3) and beta(2) mRNA by 2.4- and 1.7-fold, respectively (P < 0.05), whilst alpha(1) and alpha(2) mRNA were increased by 2.5- and 3.5-fold at 24 h and 3 h postexercise, respectively (P < 0.05). No significant change occurred for beta(1) and beta(3) mRNA, reflecting variable time-dependent responses. When the average postexercise value was contrasted to rest, mRNA increased for alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoforms, by 1.4-, 2.2-, 1.4-, 1.1-, 1.0- and 1.0-fold, respectively (P < 0.05). However, exercise did not alter the protein abundance of the alpha(1)-alpha(3) and beta(1)-beta(3) isoforms. Thus, human skeletal muscle expresses each of the Na(+),K(+)-ATPase alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoforms, evidenced at both transcription and protein levels. Whilst brief exercise increased Na(+),K(+)-ATPase isoform mRNA expression, there was no effect on isoform protein expression, suggesting that the exercise challenge was insufficient for muscle Na(+),K(+)-ATPase up-regulation.

Live high:train low increases muscle buffer capacity and submaximal cycling efficiency.

This study investigated whether hypoxic exposure increased muscle buffer capacity (beta(m)) and mechanical efficiency during exercise in male athletes. A control (CON, n=7) and a live high:train low group (LHTL, n=6) trained at near sea level (600 m), with the LHTL group sleeping for 23 nights in simulated moderate altitude (3000 m). Whole body oxygen consumption (VO2) was measured under normoxia before, during and after 23 nights of sleeping in hypoxia, during cycle ergometry comprising 4 x 4-min submaximal stages, 2-min at 5.6 +/- 0.4 W kg(-1), and 2-min 'all-out' to determine total work and VO(2peak). A vastus lateralis muscle biopsy was taken at rest and after a standardized 2-min 5.6 +/- 0.4 W kg(-1) bout, before and after LHTL, and analysed for beta(m) and metabolites. After LHTL, beta(m) was increased (18%, P < 0.05). Although work was maintained, VO(2peak) fell after LHTL (7%, P < 0.05). Submaximal VO2 was reduced (4.4%, P < 0.05) and efficiency improved (0.8%, P < 0.05) after LHTL probably because of a shift in fuel utilization. This is the first study to show that hypoxic exposure, per se, increases muscle buffer capacity. Further, reduced VO2 during normoxic exercise after LHTL suggests that improved exercise efficiency is a fundamental adaptation to LHTL.