Exercise twice-a-day potentiates markers of mitochondrial biogenesis in men.

Endurance exercise begun with reduced muscle glycogen stores seems to potentiate skeletal muscle protein abundance and gene expression. However, it is unknown whether this greater signaling responses is due to performing two exercise sessions in close proximity-as a first exercise session is necessary to reduce the muscle glycogen stores. In the present study, we manipulated the recovery duration between a first muscle glycogen-depleting exercise and a second exercise session, such that the second exercise session started with reduced muscle glycogen in both approaches but was performed either 2 or 15 hours after the first exercise session (so-called "twice-a-day" and "once-daily" approaches, respectively). We found that exercise twice-a-day increased the nuclear abundance of transcription factor EB (TFEB) and nuclear factor of activated T cells (NFAT) and potentiated the transcription of peroxisome proliferator-activated receptor-É£ coactivator 1-alpha (PGC-1α), peroxisome proliferator-activated receptor-alpha (PPARα), and peroxisome proliferator-activated receptor beta/delta (PPARß/δ) genes, in comparison with the once-daily exercise. These results suggest that part of the elevated molecular signaling reported with previous "train-low" approaches might be attributed to performing two exercise sessions in close proximity. The twice-a-day approach might be an effective strategy to induce adaptations related to mitochondrial biogenesis and fat oxidation.

Comparative physiology investigations support a role for histidine-containing dipeptides in intracellular acid-base regulation of skeletal muscle.

Histidine containing dipeptides (HCDs: carnosine, anserine and balenine) have numerous therapeutic and ergogenic properties, but there is a lack of consensus on the mechanistic pathways through which they function. Potential roles include intracellular buffering, neutralisation of reactive species, and calcium regulation. Comparative investigations of the HCD content of various species provide unique insight into their most likely mechanisms of action. This review chronologically describes how the comparative physiology studies, conducted since the beginning of the 20th century, have shaped our understanding of the physiological roles of HCDs. The investigation of a wide range of physiologically distinct species indicates that those species with a strong reliance on non-oxidative forms of energy production are abundant in HCDs. These include: whales who experience long periods of hypoxia while diving; racehorses and greyhound dogs who have highly developed sprint abilities, and chickens and turkeys whose limited capacity for flight is largely fuelled by their white, glycolytic, muscle. Additionally, a higher HCD content in the Type 2 muscle fibres of various species (which have greater capacity for non-oxidative metabolism) was consistently observed. The pKa of the HCDs render them ideally suited to act as intracellular physicochemical buffers within the pH transit range of the skeletal muscle. As such, their abundance in species which show a greater reliance on non-oxidative forms of energy metabolism, and which experience regular challenges to acid-base homeostasis, provides strong evidence that intracellular proton buffering is an important function of the HCDs in skeletal muscle.

Power-to-Strength Ratio Influences Performance Enhancement with Contrast Training.

PURPOSE: The effectiveness of contrast training (CST) for improving explosive exercise performance is modulated by various individual characteristics; however, further work is required to define these factors. METHODS: Subelite male Australian Football players (n = 22; age, 19 ± 2 yr; body mass, 80.4 ± 9.4 kg; one-repetition maximum [1-RM] half squat, 172 ± 18 kg; mean ± SD) completed two experimental trials involving two sets of squat jumps (six repetitions at 30% 1-RM) performed either alone (CTL condition) or after half squats (six repetitions at 85% 1-RM; CST condition). RESULTS: Squat jump peak power was similar between CTL and CST during set 1 (mean change: ±90% confidence interval, 2.8% ± 2.0%; effect size [ES]: ±90% confidence interval, 0.13 ± 0.09; P = 0.079) and set 2 (0.3% ± 1.7%; ES, 0.01 ± 0.08; P = 0.781). Peak power enhancement with CST was not related to maximal (1-RM half squat) strength (r = 0.001, P = 0.884), but was negatively correlated with both baseline peak power (r = 0.44, P < 0.001) and power-to-strength ratio (PSR); that is, the ratio between baseline peak power and 1-RM half squat strength (r = 0.65, P < 0.001). Using a median split, analyses were performed in participants with a low PSR (LPSR group; PSR = 15.4-19.1 W·kg; n = 11) or high PSR (HPSR group, PSR = 19.4-24.7 W·kg; n = 11). Peak power was enhanced with CST for the LPSR (8.1% ± 3.9%; ES, 0.44 ± 0.21; P = 0.004) but not HPSR (-2.1% ± 1.3%; ES, -0.14 ± 0.09; P = 0.010) groups. CONCLUSION: The PSR appears to influence the effectiveness of CST, with performance enhancement more likely in those with a lower PSR.

Caffeine Increases Work Done above Critical Power, but Not Anaerobic Work.

PURPOSE: The assumption that the curvature constant (W') of the power-duration relationship represents anaerobic work capacity is a controversial, unresolved question. We investigated if caffeine ingestion could increase total work done above critical power (CP), and if this would be accompanied by greater anaerobic energy expenditure and by an enhanced maintenance of maximal oxidative metabolic rate. METHODS: Nine men (26.6 ± 5.3 yr, V˙O2max 40.6 ± 5.8 mL·kg·min) cycled until exhaustion at different exercise intensities on different days to determine the CP and W'. On separated days, participants cycled until exhaustion in the severe-intensity domain (136% ± 7% of CP) after ingesting either caffeine (5 mg·kg body mass) or a placebo. RESULTS: Time to exhaustion was 34% longer with caffeine compared with placebo, and this was accompanied by a greater work done above CP (23.7 ± 5.7 vs 17.5 ± 3.6 kJ; 130% ± 30% vs 95% ± 14% of W', P < 0.01). Caffeine increased the aerobic energy expenditure (296.4 ± 91.0 vs 210.2 ± 71.9 kJ, P < 0.01), but not anaerobic lactic, anaerobic alactic, and total anaerobic (lactic + alactic) energy expenditure. The end values of heart rate and ventilation were higher with caffeine, but the V˙O2 end was similar between conditions and was not different from V˙O2max. Caffeine did not change time to reach V˙O2max but increased time maintained at V˙O2max (199.3 ± 105.9 vs 111.9 ± 87.1 s, P < 0.05). CONCLUSIONS: Caffeine increased total work done above CP, but this was not associated with greater anaerobic work. Rather, this was associated with a higher tolerance to maintain exercise at maximal oxidative metabolic rate.

Acidosis, but Not Alkalosis, Affects Anaerobic Metabolism and Performance in a 4-km Time Trial.

PURPOSE: This study aimed to determine the effect of preexercise metabolic acidosis and alkalosis on power output (PO) and aerobic and anaerobic energy expenditure during a 4-km cycling time trial (TT). METHODS: Eleven recreationally trained cyclists (V˙O2peak 54.1 ± 9.3 mL·kg·min) performed a 4-km TT 100 min after ingesting in a double-blind matter 0.15 g·kg of body mass of ammonium chloride (NH4Cl, acidosis), 0.3 g·kg of sodium bicarbonate (NaHCO3, alkalosis), or 0.15 g·kg of CaCO3 (placebo). A preliminary study (n = 7) was conducted to establish the optimal doses to promote the desirable preexercise blood pH alterations without gastrointestinal distress. Data for PO, aerobic and anaerobic energy expenditure, and blood and respiratory parameters were averaged for each 1 km and compared between conditions using two-way repeated-measures ANOVA (condition and distance factors). Gastrointestinal discomfort was analyzed qualitatively. RESULTS: Compared with placebo (pH 7.37 ± 0.02, [HCO3]: 27.5 ± 2.6 mmol·L), the NaHCO3 ingestion resulted in a preexercise blood alkalosis (pH +0.06 ± 0.04, [HCO3]: +4.4 ± 2.0 mmol·L, P < 0.05), whereas NH4Cl resulted in a blood acidosis (pH -0.05 ± 0.03, [HCO3]: -4.8 ± 2.1 mmol·L, P < 0.05). Anaerobic energy expenditure rate and PO were reduced throughout the trial in NH4Cl compared with placebo and NaHCO3, resulting in a lower total anaerobic work and impaired performance (P < 0.05). Plasma lactate, V˙CO2, and end-tidal CO2 partial pressure were lower and the V˙E/V˙CO2 higher throughout the trial in NH4Cl compared with placebo and NaHCO3 (P < 0.05). There was no difference between NaHCO3 and placebo for any of these variables (P > 0.05). Minimal gastrointestinal distress was noted in all conditions. CONCLUSION: Preexercise acidosis, but not alkalosis, affects anaerobic metabolism and PO during a 4-km cycling TT.

Similar mitochondrial signaling responses to a single bout of continuous or small-sided-games-based exercise in sedentary men.

This study assessed the mitochondrial related signaling responses to a single bout of noncontact, modified football (touch rugby), played as small-sided games (SSG), or cycling (CYC) exercise in sedentary, obese, middle-aged men. In a randomized, crossover design, nine middle-aged, sedentary, obese men completed two, 40-min exercise conditions (CYC and SSG) separated by a 21-day recovery period. Heart rate (HR) and ratings of perceived exertion (RPE) were collected during each bout. Needle biopsies from the vastus lateralis muscle were collected at rest and 30 and 240 min postexercise for analysis of protein content and phosphorylation (PGC-1α, SIRT1, p53, p53Ser15, AMPK, AMPKThr172, CAMKII, CAMKIIThr286, p38MAPK, and p38MAPKThr180/Tyr182) and mRNA expression (PGC-1α, p53, NRF1, NRF2, Tfam, and cytochrome c). A main effect of time effect for both conditions was evident for HR, RPE, and blood lactate (P < 0.05), with no condition by time interaction (P > 0.05). Both conditions increased PGC1-α protein and mRNA expression at 240 min (P < 0.05). AMPKThr172 increased 30 min post CYC (P < 0.05), with no change in SSG (P > 0.05). CYC increased p53 protein content at 240 min to a greater extent than SSG (P < 0.05). mRNA expression of NRF2 decreased in both conditions (P < 0.05). No condition by time interactions were evident for mRNA expression of Tfam, NRF1, cytochrome c, and p53. The similar PGC-1α response between intensity-matched conditions suggests both conditions are of similar benefit for stimulating mitochondrial biogenesis. Differences between conditions regarding fluctuation in exercise intensity and type of muscle contraction may explain the increase of p53 and AMPK within CYC and not SSG (noncontact, modified football).

Effect of Creatine Loading on Oxygen Uptake during a 1-km Cycling Time Trial.

PURPOSE: For the first time, we investigated the effects of altering cellular metabolic capacitance, via a 5-d creatine (Cr) loading protocol (20 g·d⁻¹), on oxygen uptake (VO2), accumulated oxygen deficit, muscle recruitment, and performance during a 1-km cycling time trial. METHODS: In a double-blind, randomized, placebo-controlled design, 19 amateur cyclists were allocated to a Cr (n = 10, VO2peak = 56.0 ± 7.8 mL·kg⁻¹·min⁻¹) or placebo (n = 9, VO2peak = 56.0 ± 8.4 mL·kg⁻¹·min⁻¹) group, and performed a 1-km cycling time trial before and after the supplementation period. RESULTS: Body mass was significantly increased in the Cr group (P < 0.05), but not in the placebo group. Participants adopted an "all-out" pacing strategy in both groups. However, Cr loading reduced VO2 immediately after the beginning (12th to 23th seconds), and this was accompanied by a reduced aerobic and increased anaerobic contribution. The VO2 mean response time was slower (pre: 17.2 ± 5.6 s vs post: 19.9 ± 4.6 s), the total O2 uptake was reduced (pre: 4.64 ± 0.59 L vs post: 4.47 ± 0.53 L), and the oxygen deficit was increased (pre: 0.82 ± 0.27 L vs post: 0.98 ± 0.25 L) after Cr loading. No differences were observed in the placebo group for these variables. Plasma lactate and integrated electromyography were not altered in either group, nor was the time to complete the trial (Cr group: pre: 89.1 ± 6.7 s vs post 89.1 ± 6.2 s and placebo group: pre 85.9 ± 4.9 s vs post 87.0 ± 5.4 s). CONCLUSION: Cr loading slows the V˙O2 response and increases the anaerobic contribution during a 1-km cycling time trial.

Effect of time of day on performance, hormonal and metabolic response during a 1000-M cycling time trial.

The aim of this study was to determine the effect of time of day on performance, pacing, and hormonal and metabolic responses during a 1000-m cycling time-trial. Nine male, recreational cyclists visited the laboratory four times. During the 1st visit the participants performed an incremental test and during the 2nd visit they performed a 1000-m cycling familiarization trial. On the 3rd and 4th visits, the participants performed a 1000-m TT at either 8 am or 6 pm, in randomized, repeated-measures, crossover design. The time to complete the time trial was lower in the evening than in the morning (88.2±8.7 versus 94.7±10.9 s, respectively, p<0.05), but there was no significant different in pacing. However, oxygen uptake and aerobic mechanical power output at 600 and 1000 m tended to be higher in the evening (p<0.07 and 0.09, respectively). There was also a main effect of time of day for insulin, cortisol, and total and free testosterone concentration, which were all higher in the morning (+60%, +26%, +31% and +22%, respectively, p<0.05). The growth hormone, was twofold higher in the evening (p<0.05). The plasma glucose was ∼11% lower in the morning (p<0.05). Glucagon, norepinephrine, epinephrine and lactate were similar for the morning and evening trials (p>0.05), but the norepinephrine response to the exercise was increased in the morning (+46%, p<0.05), and it was accompanied by a 5-fold increase in the response of glucose. Muscle recruitment, as measured by electromyography, was similar between morning and evening trials (p>0.05). Our findings suggest that performance was improved in the evening, and it was accompanied by an improved hormonal and metabolic milieu.

Prior low- or high-intensity exercise alters pacing strategy, energy system contribution and performance during a 4-km cycling time trial.

We analyzed the influence of prior exercise designed to reduce predominantly muscle glycogen in either type I or II fibers on pacing and performance during a 4-km cycling time trial (TT). After preliminary and familiarization trials, in a randomized, repeated-measures crossover design, ten amateur cyclists performed: 1) an exercise designed to reduce glycogen of type I muscle fibers, followed by a 4-km TT (EX-FIB I); 2) an exercise designed to reduce glycogen of type II muscle fibers, followed by a 4-km TT (EX-FIB II) and; 3) a 4-km TT, without the prior exercise (CONT). The muscle-glycogen-reducing exercise in both EX-FIB I and EX-FIB II was performed in the evening, ∼12 h before the 4-km TT. Performance time was increased and power output (PO) was reduced in EX-FIB I (432.8±8.3 s and 204.9±10.9 W) and EX-FIB II (428.7±6.7 s and 207.5±9.1 W) compared to CONT (420.8±6.4 s and 218.4±9.3 W; P<0.01), without a difference between EX-FIB I and EX-FIB II (P>0.05). The PO was lower in EX-FIB I than in CONT at the beginning and middle of the trial (P<0.05). The mean aerobic contribution during EX-FIB I was also significantly lower than in CONT (P<0.05), but there was no difference between CONT and EX-FIB II or between EX-FIB I and EX-FIB II (P>0.05). The integrated electromyography was unchanged between conditions (P>0.05). Performance may have been impaired in EX-FIB I due a more conservative pacing at the beginning and middle, which was associated with a reduced aerobic contribution. In turn, the PO profile adopted in EX-FIB II was also reduced throughout the trial, but the impairment in performance may be attributed to a reduced glycolytic contribution (i.e. reduced lactate accumulation).

Caffeine alters anaerobic distribution and pacing during a 4000-m cycling time trial.

The purpose of the present study was to investigate the effects of caffeine ingestion on pacing strategy and energy expenditure during a 4000-m cycling time-trial (TT). Eight recreationally-trained male cyclists volunteered and performed a maximal incremental test and a familiarization test on their first and second visits, respectively. On the third and fourth visits, the participants performed a 4000-m cycling TT after ingesting capsules containing either caffeine (5 mg.kg(-1) of body weight, CAF) or cellulose (PLA). The tests were applied in a double-blind, randomized, repeated-measures, cross-over design. When compared to PLA, CAF ingestion increased mean power output [219.1±18.6 vs. 232.8±21.4 W; effect size (ES)  = 0.60 (95% CI = 0.05 to 1.16), p = 0.034] and reduced the total time [419±13 vs. 409±12 s; ES = -0.71 (95% CI = -0.09 to -1.13), p = 0.026]. Furthermore, anaerobic contribution during the 2200-, 2400-, and 2600-m intervals was significantly greater in CAF than in PLA (p<0.05). However, the mean anaerobic [64.9±20.1 vs. 57.3±17.5 W] and aerobic [167.9±4.3 vs. 161.8±11.2 W] contributions were similar between conditions (p>0.05). Similarly, there were no significant differences between CAF and PLA for anaerobic work (26363±7361 vs. 23888±6795 J), aerobic work (68709±2118 vs. 67739±3912 J), or total work (95245±8593 vs. 91789±7709 J), respectively. There was no difference for integrated electromyography, blood lactate concentration, heart rate, and ratings of perceived exertion between the conditions. These results suggest that caffeine increases the anaerobic contribution in the middle of the time trial, resulting in enhanced overall performance.

Caffeine increases anaerobic work and restores cycling performance following a protocol designed to lower endogenous carbohydrate availability.

The purpose this study was to examine the effects of caffeine ingestion on performance and energy expenditure (anaerobic and aerobic contribution) during a 4-km cycling time trial (TT) performed after a carbohydrate (CHO) availability-lowering exercise protocol. After preliminary and familiarization trials, seven amateur cyclists performed three 4-km cycling TT in a double-blind, randomized and crossover design. The trials were performed either after no previous exercise (CON), or after a CHO availability-lowering exercise protocol (DEP) performed in the previous evening, followed by either placebo (DEP-PLA) or 5 mg.kg(-1) of caffeine intake (DEP-CAF) 1 hour before the trial. Performance was reduced (-2.1%) in DEP-PLA vs CON (421.0±12.3 vs 412.4±9.7 s). However, performance was restored in DEP-CAF (404.6±17.1 s) compared with DEP-PLA, while no differences were found between DEP-CAF and CON. The anaerobic contribution was increased in DEP-CAF compared with both DEP-PLA and CON (67.4±14.91, 47. 3±14.6 and 55.3±14.0 W, respectively), and this was more pronounced in the first 3 km of the trial. Similarly, total anaerobic work was higher in DEP-CAF than in the other conditions. The integrated electromyographic activity, plasma lactate concentration, oxygen uptake, aerobic contribution and total aerobic work were not different between the conditions. The reduction in performance associated with low CHO availability is reversed with caffeine ingestion due to a higher anaerobic contribution, suggesting that caffeine could access an anaerobic "reserve" that is not used under normal conditions.