Effect of consecutive repeated sprint and resistance exercise bouts on acute adaptive responses in human skeletal muscle

Interference between concurrent resistance and endurance exercise: molecular bases and the role of individual training variables

Concurrent training is defined as simultaneously incorporating both resistance and endurance exercise within a periodized training regime. Despite the potential additive benefits of combining these divergent exercise modes with regards to disease prevention and athletic performance, current evidence suggests that this approach may attenuate gains in muscle mass, strength, and power compared with undertaking resistance training alone. This has been variously described as the interference effect or concurrent training effect. In recent years, understanding of the molecular mechanisms mediating training adaptation in skeletal muscle has emerged and provided potential mechanistic insight into the concurrent training effect. Although it appears that various molecular signaling responses induced in skeletal muscle by endurance exercise can inhibit pathways regulating protein synthesis and stimulate protein breakdown, human studies to date have not observed such molecular 'interference' following acute concurrent exercise that might explain compromised muscle hypertrophy following concurrent training. However, given the multitude of potential concurrent training variables and the limitations of existing evidence, the potential roles of individual training variables in acute and chronic interference are not fully elucidated. The present review explores current evidence for the molecular basis of the specificity of training adaptation and the concurrent interference phenomenon. Additionally, insights provided by molecular and performance-based concurrent training studies regarding the role of individual training variables (i.e., within-session exercise order, between-mode recovery, endurance training volume, intensity, and modality) in the concurrent interference effect are discussed, along with the limitations of our current understanding of this complex paradigm.

Sex differences in acute translational repressor 4E-BP1 activity and sprint performance in response to repeated-sprint exercise in team sport athletes

OBJECTIVES

The physiological requirements underlying soccer-specific exercise are incomplete and sex-based comparisons are sparse. The aim of this study was to determine the effects of a repeated-sprint protocol on the translational repressor 4E-BP1 and sprint performance in male and female soccer players.

DESIGN

Cross-over design involving eight female and seven male university soccer players.

METHODS

Participants performed four bouts of 6 × 30-m maximal sprints spread equally over 40 min. Heart rate, sprint time and sprint decrement were measured for each sprint and during the course of each bout. Venous blood samples and muscle biopsies from the vastus lateralis were taken at rest, at 15 min and 2h post-exercise.

RESULTS

While males maintained a faster mean sprint time for each bout (P < 0.05) females exhibited a greater decrement in sprint performance for each bout (P < 0.05), indicating a superior maintenance of sprint performance in males, with no sex differences for heart rate or lactate. Muscle analyses revealed sex differences in resting total (P < 0.05) and phosphorylated (P < 0.05) 4E-BP1 Thr37/46, and 15 min post-exercise the 4E-BP1 Thr37/46 ratio decreased below resting levels in males only (P < 0.05), indicative of a decreased translation initiation following repeated sprints.

CONCLUSIONS

We show that females have a larger sprint decrement indicating that males have a superior ability to recover sprint performance. Sex differences in resting 4E-BP1 Thr37/46 suggest diversity in the training-induced phenotype of the muscle of males and females competing in equivalent levels of team-sport competition.

The order of exercise during concurrent training for rehabilitation does not alter acute genetic expression, mitochondrial enzyme activity or improvements in muscle function

Concurrent exercise combines different modes of exercise (e.g., aerobic and resistance) into one training protocol, providing stimuli meant to increase muscle strength, aerobic capacity and mass. As disuse is associated with decrements in strength, aerobic capacity and muscle size concurrent training is an attractive modality for rehabilitation. However, interference between the signaling pathways may result in preferential improvements for one of the exercise modes. We recruited 18 young adults (10 ♂, 8 ♀) to determine if order of exercise mode during concurrent training would differentially affect gene expression, protein content and measures of strength and aerobic capacity after 2 weeks of knee-brace induced disuse. Concurrent exercise sessions were performed 3x/week for 6 weeks at gradually increasing intensities either with endurance exercise preceding (END>RES) or following (RES>END) resistance exercise. Biopsies were collected from the vastus lateralis before, 3 h after the first exercise bout and 48 h after the end of training. Concurrent exercise altered the expression of genes involved in mitochondrial biogenesis (PGC-1α, PRC, PPARγ), hypertrophy (PGC-1α4, REDD2, Rheb) and atrophy (MuRF-1, Runx1), increased electron transport chain complex protein content, citrate synthase and mitochondrial cytochrome c oxidase enzyme activity, muscle mass, maximum isometric strength and VO_2peak. However, the order in which exercise was completed (END>RES or RES>END) only affected the protein content of mitochondrial complex II subunit. In conclusion, concurrent exercise training is an effective modality for the rehabilitation of the loss of skeletal muscle mass, maximum strength, and peak aerobic capacity resulting from disuse, regardless of the order in which the modes of exercise are performed.

Single muscle fiber gene expression with run taper

This study evaluated gene expression changes in gastrocnemius slow-twitch myosin heavy chain I (MHC I) and fast-twitch (MHC IIa) muscle fibers of collegiate cross-country runners (n = 6, 20±1 y, VO_2max = 70±1 ml•kg⁻¹•min⁻¹) during two distinct training phases. In a controlled environment, runners performed identical 8 kilometer runs (30∶18±0∶30 min:s, 89±1% HR_max) while in heavy training (∼72 km/wk) and following a 3 wk taper. Training volume during the taper leading into peak competition was reduced ∼50% which resulted in improved race times and greater cross-section and improved function of MHC IIa fibers. Single muscle fibers were isolated from pre and 4 hour post run biopsies in heavily trained and tapered states to examine the dynamic acute exercise response of the growth-related genes Fibroblast growth factor-inducible 14 (FN14), Myostatin (MSTN), Heat shock protein 72 (HSP72), Muscle ring-finger protein-1 (MURF1), Myogenic factor 6 (MRF4), and Insulin-like growth factor 1 (IGF1) via qPCR. FN14 increased 4.3-fold in MHC IIa fibers with exercise in the tapered state (P<0.05). MSTN was suppressed with exercise in both fiber types and training states (P<0.05) while MURF1 and HSP72 responded to running in MHC IIa and I fibers, respectively, regardless of training state (P<0.05). Robust induction of FN14 (previously shown to strongly correlate with hypertrophy) and greater overall transcriptional flexibility with exercise in the tapered state provides an initial molecular basis for fast-twitch muscle fiber performance gains previously observed after taper in competitive endurance athletes.

Nutritional strategies to support concurrent training

Concurrent training (the combination of endurance exercise to resistance training) is a common practice for athletes looking to maximise strength and endurance. Over 20 years ago, it was first observed that performing endurance exercise after resistance exercise could have detrimental effects on strength gains. At the cellular level, specific protein candidates have been suggested to mediate this training interference; however, at present, the physiological reason(s) behind the concurrent training effect remain largely unknown. Even less is known regarding the optimal nutritional strategies to support concurrent training and whether unique nutritional approaches are needed to support endurance and resistance exercise during concurrent training approaches. In this review, we will discuss the importance of protein supplementation for both endurance and resistance training adaptation and highlight additional nutritional strategies that may support concurrent training. Finally, we will attempt to synergise current understanding of the interaction between physiological responses and nutritional approaches into practical recommendations for concurrent training.

The order of concurrent endurance and resistance exercise modifies mTOR signaling and protein synthesis in rat skeletal muscle

Concurrent training, a combination of endurance (EE) and resistance exercise (RE) performed in succession, may compromise the muscle hypertrophic adaptations induced by RE alone. However, little is known about the molecular signaling interactions underlying the changes in skeletal muscle adaptation during concurrent training. Here, we used an animal model to investigate whether EE before or after RE affects the molecular signaling associated with muscle protein synthesis, specifically the interaction between RE-induced mammalian target of rapamycin complex 1 (mTORC1) signaling and EE-induced AMP-activated protein kinase (AMPK) signaling. Male Sprague-Dawley rats were divided into five groups: an EE group (treadmill, 25 m/min, 60 min), an RE group (maximum isometric contraction via percutaneous electrical stimulation for 3 × 10 s, 5 sets), an EE before RE group, an EE after RE group, and a nonexercise control group. Phosphorylation of p70S6K, a marker of mTORC1 activity, was significantly increased 3 h after RE in both the EE before RE and EE after RE groups, but the increase was smaller in latter. Furthermore, protein synthesis was greatly increased 6 h after RE in the EE before RE group. Increases in the phosphorylation of AMPK and Raptor were observed only in the EE after RE group. Akt and mTOR phosphorylation were increased in both groups, with no between-group differences. Our results suggest that the last bout of exercise dictates the molecular responses and that mTORC1 signaling induced by any prior bout of RE may be downregulated by a subsequent bout of EE.

Alcohol ingestion impairs maximal post-exercise rates of myofibrillar protein synthesis following a single bout of concurrent training

Introduction

The culture in many team sports involves consumption of large amounts of alcohol after training/competition. The effect of such a practice on recovery processes underlying protein turnover in human skeletal muscle are unknown. We determined the effect of alcohol intake on rates of myofibrillar protein synthesis (MPS) following strenuous exercise with carbohydrate (CHO) or protein ingestion.

Methods

In a randomized cross-over design, 8 physically active males completed three experimental trials comprising resistance exercise (8×5 reps leg extension, 80% 1 repetition maximum) followed by continuous (30 min, 63% peak power output (PPO)) and high intensity interval (10×30 s, 110% PPO) cycling. Immediately, and 4 h post-exercise, subjects consumed either 500 mL of whey protein (25 g; PRO), alcohol (1.5 g·kg body mass⁻¹, 12±2 standard drinks) co-ingested with protein (ALC-PRO), or an energy-matched quantity of carbohydrate also with alcohol (25 g maltodextrin; ALC-CHO). Subjects also consumed a CHO meal (1.5 g CHO·kg body mass⁻¹) 2 h post-exercise. Muscle biopsies were taken at rest, 2 and 8 h post-exercise.

Results

Blood alcohol concentration was elevated above baseline with ALC-CHO and ALC-PRO throughout recovery (P<0.05). Phosphorylation of mTOR^Ser2448 2 h after exercise was higher with PRO compared to ALC-PRO and ALC-CHO (P<0.05), while p70S6K phosphorylation was higher 2 h post-exercise with ALC-PRO and PRO compared to ALC-CHO (P<0.05). Rates of MPS increased above rest for all conditions (∼29–109%, P<0.05). However, compared to PRO, there was a hierarchical reduction in MPS with ALC-PRO (24%, P<0.05) and with ALC-CHO (37%, P<0.05).

Conclusion

We provide novel data demonstrating that alcohol consumption reduces rates of MPS following a bout of concurrent exercise, even when co-ingested with protein. We conclude that alcohol ingestion suppresses the anabolic response in skeletal muscle and may therefore impair recovery and adaptation to training and/or subsequent performance.

Molecular mechanisms of muscle plasticity with exercise

The skeletal muscle phenotype is subject to considerable malleability depending on use. Low-intensity endurance type exercise leads to qualitative changes of muscle tissue characterized mainly by an increase in structures supporting oxygen delivery and consumption. High-load strength-type exercise leads to growth of muscle fibers dominated by an increase in contractile proteins. In low-intensity exercise, stress-induced signaling leads to transcriptional upregulation of a multitude of genes with Ca(2+) signaling and the energy status of the muscle cells sensed through AMPK being major input determinants. Several parallel signaling pathways converge on the transcriptional co-activator PGC-1α, perceived as being the coordinator of much of the transcriptional and posttranscriptional processes. High-load training is dominated by a translational upregulation controlled by mTOR mainly influenced by an insulin/growth factor-dependent signaling cascade as well as mechanical and nutritional cues. Exercise-induced muscle growth is further supported by DNA recruitment through activation and incorporation of satellite cells. Crucial nodes of strength and endurance exercise signaling networks are shared making these training modes interdependent. Robustness of exercise-related signaling is the consequence of signaling being multiple parallel with feed-back and feed-forward control over single and multiple signaling levels. We currently have a good descriptive understanding of the molecular mechanisms controlling muscle phenotypic plasticity. We lack understanding of the precise interactions among partners of signaling networks and accordingly models to predict signaling outcome of entire networks. A major current challenge is to verify and apply available knowledge gained in model systems to predict human phenotypic plasticity.

Concurrent repeated-sprint and resistance training with superimposed vibrations in rugby players

PURPOSE

To examine the effect of repeated-sprint training (RST) vs combined RST and resistance training with superimposed vibrations on repeated-sprint ability (RSA) and lower-body power output in male rugby players.

METHODS

Players were divided into 2 training groups. One group performed RST (n = 10) 2 d/wk and the other performed RST 1 d/wk and squat resistance training with superimposed vibrations on the second day (RS+ST; n = 10). The squat training was carried out with a volume similar (ie, number of sets and repetitions) to that of the RST. The training period lasted 6 wk, and it was carried out as a supplement to the regular rugby training sessions.

RESULTS

Substantial improvements in RSA mean time (RSA(mean); +2.3%/ES: 0.77 vs +4.1%/ES: 0.91), RSA percent decrement (%Dec; -25.6%/ES: 1.70 vs -23.2%/ES: 0.99), and squat absolute power output (+5.0%/ES:0.36 vs +17.2%/ES: 0.93) were obtained in RST and RS+ST, respectively. Substantial improvements in RSA best time (RSA(best); +2.6%/ES: 0.61) and squat power output normalized to body mass (+18.6%/ES: 0.76) only occurred in RS+ST. Both pretest and posttest RSA(mean) were largely correlated with the RSA(best). However, there were only unclear, small to moderate correlations between individual changes in squat power output and either RSA(mean) or RSA(best).

CONCLUSION

Combined RST and resistance training induced improvements of greater magnitude in both repeated-sprint performance and muscle power output than the RST alone. The lack of substantial correlations between individual changes in repeated-sprint and muscle-power performance suggests that the same subjects were not systematically low or high responders to both RST and strength training.

Resistance exercise induced mTORC1 signaling is not impaired by subsequent endurance exercise in human skeletal muscle

The current dogma is that the muscle adaptation to resistance exercise is blunted when combined with endurance exercise. The suggested mechanism (based on rodent experiments) is that activation of adenosine monophosphate-activated protein kinase (AMPK) during endurance exercise impairs muscle growth through inhibition of the mechanistic target of rapamycin complex 1 (mTORC1). The purpose of this study was to investigate potential interference of endurance training on the signaling pathway of resistance training [mTORC1 phosphorylation of ribosomal protein S6 kinase 1 (S6K1)] in human muscle. Ten healthy and moderately trained male subjects performed on two separate occasions either acute high-intensity and high-volume resistance exercise (leg press, R) or R followed by 30 min of cycling (RE). Muscle biopsies were collected before and 1 and 3 h post resistance exercise. Phosphorylation of mTOR (Ser²⁴⁴⁸) increased 2-fold (P < 0.05) and that of S6K1 (Thr³⁸⁹) 14-fold (P < 0.05), with no difference between R and RE. Phosphorylation of eukaryotic elongation factor 2 (eEF2, Thr⁵⁶) was reduced ~70% during recovery in both trials (P < 0.05). An interesting finding was that phosphorylation of AMPK (Thr¹⁷²) and acetyl-CoA carboxylase (ACC, Ser⁷⁹) decreased ~30% and ~50%, respectively, 3 h postexercise (P < 0.05). Proliferator-activated receptor-γ coactivator-1 (PGC-1α) mRNA increased more after RE (6.5-fold) than after R (4-fold) (RE vs. R: P < 0.01) and was the only gene expressed differently between trials. These data show that the signaling of muscle growth through the mTORC1-S6K1 axis after heavy resistance exercise is not inhibited by subsequent endurance exercise. It is also suggested that prior activation of mTORC1 signaling may repress subsequent phosphorylation of AMPK.

Aerobic exercise alters skeletal muscle molecular responses to resistance exercise

PURPOSE

This study assessed the influence of an acute aerobic exercise bout on molecular responses to subsequent resistance exercise (RE).

METHODS

Nine physically active men performed a 45-min one-legged cycle ergometry exercise and 4 × 7 maximal concentric-eccentric knee extensions for each leg 6 h later. Thus, one limb was subjected to aerobic and resistance exercise (AE+RE), and the contralateral limb to resistance exercise (RE) only. Knee extensor peak power was determined. Biopsies were obtained from the m vastus lateralis before (PRE) and 15 min (POST1) and 3 h after RE. Analysis determined glycogen content, mRNA levels (vascular endothelial growth factor, peroxisome proliferator-activated receptor-γ coactivator-1, muscle RING-finger protein-1, atrogin-1, myostatin), and phosphorylated proteins (mammalian target of rapamycin, p70S6 kinase, ribosomal protein S6, eukaryotic elongation factor 2).

RESULTS

Peak power was similar in AE + RE and RE. After RE, the time course of glycogen utilization and protein signaling was similar across legs. However, phosphorylation of mammalian target of rapamycin and p70S6 kinase was elevated in AE + RE versus RE (main effect, P < 0.05). Vascular endothelial growth factor and peroxisome proliferator-activated receptor-γ coactivator-1 were higher in AE + RE than in RE at PRE and POST1 (P < 0.05). Myostatin was lower in AE + RE versus RE at PRE and POST1 (P < 0.05) and downregulated after resistance exercise only. Atrogin-1 was higher in AE + RE than in RE at PRE and POST1 (P < 0.05) and decreased after RE in AE + RE. Muscle RING-finger protein-1 was similar across legs. No difference for any marker was evident 3 h after RE.

CONCLUSIONS

These results suggest that acute aerobic exercise alters molecular events regulating muscle protein turnover during the early recovery period from subsequent RE.

Short-term intensified cycle training alters acute and chronic responses of PGC1α and Cytochrome C oxidase IV to exercise in human skeletal muscle

Reduced activation of exercise responsive signalling pathways have been reported in response to acute exercise after training; however little is known about the adaptive responses of the mitochondria. Accordingly, we investigated changes in mitochondrial gene expression and protein abundance in response to the same acute exercise before and after 10-d of intensive cycle training. Nine untrained, healthy participants (mean±SD; VO_2peak 44.1±17.6 ml/kg/min) performed a 60 min bout of cycling exercise at 164±18 W (72% of pre-training VO_2peak). Muscle biopsies were obtained from the vastus lateralis muscle at rest, immediately and 3 h after exercise. The participants then underwent 10-d of cycle training which included four high-intensity interval training sessions (6×5 min; 90–100% VO_2peak) and six prolonged moderate-intensity sessions (45–90 min; 75% VO_2peak). Participants repeated the pre-training exercise trial at the same absolute work load (64% of pre-training VO_2peak). Muscle PGC1-α mRNA expression was attenuated as it increased by 11- and 4- fold (P<0.001) after exercise pre- and post-training, respectively. PGC1-α protein expression increased 1.5 fold (P<0.05) in response to exercise pre-training with no further increases after the post-training exercise bout. RIP140 protein abundance was responsive to acute exercise only (P<0.01). COXIV mRNA (1.6 fold; P<0.01) and COXIV protein expression (1.5 fold; P<0.05) were increased by training but COXIV protein expression was decreased (20%; P<0.01) by acute exercise pre- and post-training. These findings demonstrate that short-term intensified training promotes increased mitochondrial gene expression and protein abundance. Furthermore, acute indicators of exercise-induced mitochondrial adaptation appear to be blunted in response to exercise at the same absolute intensity following short-term training.

Aerobic exercise does not compromise muscle hypertrophy response to short-term resistance training

This study tested the hypothesis that chronic aerobic and resistance exercise (AE+RE) would elicit greater muscle hypertrophy than resistance exercise only (RE). Ten men (25 ± 4 yr) performed 5 wk unilateral knee extensor AE+RE. The opposing limb was subjected to RE. AE completed 6 hr prior to RE consisted of ~45 min one-legged cycle ergometry. RE comprised 4 × 7 maximal concentric-eccentric knee extensions. Various indexes of in vivo knee extensor function were measured before and after training. Magnetic resonance imaging (MRI) assessed m. quadricep femoris (QF) cross-sectional area (CSA), volume, and signal intensity (SI). Biopsies obtained from m. vastus lateralis determined fiber CSA, enzyme levels, and gene expression of myostatin, atrogin-1, MuRF-1, PGC-1α, and VEGF. Increases (P < 0.05) in isometric strength and peak power, respectively, were comparable in AE+RE (9 and 29%) and RE (11 and 24%). AE+RE showed greater increase (14%; P < 0.05) in QF volume than RE (8%). Muscle fiber CSA increased 17% after AE+RE (P < 0.05) and 9% after RE (P > 0.05). QF SI increased (12%; P < 0.05) after AE+RE, but not RE. Neither AE+RE nor RE showed altered mRNA levels. Citrate synthase activity increased (P < 0.05) after AE+RE. The results suggest that the increased aerobic capacity shown with AE+RE was accompanied by a more robust increase in muscle size compared with RE. Although this response was not carried over to greater improvement in muscle function, it remains that intense AE can be executed prior to RE without compromising performance outcome.

New records in aerobic power among octogenarian lifelong endurance athletes

We examined whole body aerobic capacity and myocellular markers of oxidative metabolism in lifelong endurance athletes [n = 9, 81 ± 1 yr, 68 ± 3 kg, body mass index (BMI) = 23 ± 1 kg/m(2)] and age-matched, healthy, untrained men (n = 6; 82 ± 1 y, 77 ± 5 kg, BMI = 26 ± 1 kg/m(2)). The endurance athletes were cross-country skiers, including a former Olympic champion and several national/regional champions, with a history of aerobic exercise and participation in endurance events throughout their lives. Each subject performed a maximal cycle test to assess aerobic capacity (VO(2max)). Subjects had a resting vastus lateralis muscle biopsy to assess oxidative enzymes (citrate synthase and βHAD) and molecular (mRNA) targets associated with mitochondrial biogenesis [peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) and mitochondrial transcription factor A (Tfam)]. The octogenarian athletes had a higher (P < 0.05) absolute (2.6 ± 0.1 vs. 1.6 ± 0.1 l/min) and relative (38 ± 1 vs. 21 ± 1 ml·kg(-1)·min(-1)) VO(2max), ventilation (79 ± 3 vs. 64 ± 7 l/min), heart rate (160 ± 5 vs. 146 ± 8 beats per minute), and final workload (182 ± 4 vs. 131 ± 14 W). Skeletal muscle oxidative enzymes were 54% (citrate synthase) and 42% (βHAD) higher (P < 0.05) in the octogenarian athletes. Likewise, basal PGC-1α and Tfam mRNA were 135% and 80% greater (P < 0.05) in the octogenarian athletes. To our knowledge, the VO(2max) of the lifelong endurance athletes is the highest recorded in humans >80 yr of age and comparable to nonendurance trained men 40 years younger. The superior cardiovascular and skeletal muscle health profile of the octogenarian athletes provides a large functional reserve above the aerobic frailty threshold and is associated with lower risk for disability and mortality.

Concurrent aerobic exercise interferes with the satellite cell response to acute resistance exercise

The addition of aerobic exercise (AE) to a resistance exercise (RE) program (concurrent exercise, CE) can interfere with maximum muscle fiber growth achieved with RE. Further, CE appears to markedly affect the growth of myosin heavy chain (MHC) I, but not MHC IIa fibers. The mechanism responsible for this “interference” is unclear. Satellite cell (SC) responsiveness to exercise appears to influence muscle adaptation but has not yet been examined following acute concurrent exercise. Thus, we assessed the fiber-type-specific SC response to RE, AE, and CE exercise. Eight college-aged males completed the following two exercise trials: the RE trial, which consisted of unilateral leg extensions and presses (4 sets ≥ 10 repetitions: 75% 1 repetition maximum, RM); and the AE/CE trial, which included an identical RE protocol with the opposite leg, immediately followed by subjects cycling for 90 min (60% Wmax). Muscle biopsies were obtained from the vastus lateralis before and 4 days after each session. Samples were cross-sectioned, stained with antibodies against NCAM, Ki-67, and MHC I, counterstained with DAPI, and analyzed for SC density (SC per fiber), SC activation, and fiber type. SC density increased to a greater extent following RE (38 ± 10%), compared with CE (−6 ± 8%). Similarly, MHC I muscle fiber SC density displayed a greater increase following RE (46 ± 14%), compared with AE (−7 ± 17%) and CE (−8 ± 8%). Our data indicate that the SC response to RE is blunted when immediately followed by AE, at least in MHC I muscle fibers, and possibly MHC II fibers. This suggests that the physiological environment evoked by AE might attenuate the eventual addition of myonuclei important for maximum muscle fiber growth and consequent force-producing capacity.

Repeated-sprint ability - part II: recommendations for training

Short-duration sprints, interspersed with brief recoveries, are common during most team sports. The ability to produce the best possible average sprint performance over a series of sprints (≤10 seconds), separated by short (≤60 seconds) recovery periods has been termed repeated-sprint ability (RSA). RSA is therefore an important fitness requirement of team-sport athletes, and it is important to better understand training strategies that can improve this fitness component. Surprisingly, however, there has been little research about the best training methods to improve RSA. In the absence of strong scientific evidence, two principal training theories have emerged. One is based on the concept of training specificity and maintains that the best way to train RSA is to perform repeated sprints. The second proposes that training interventions that target the main factors limiting RSA may be a more effective approach. The aim of this review (Part II) is to critically analyse training strategies to improve both RSA and the underlying factors responsible for fatigue during repeated sprints (see Part I of the preceding companion article). This review has highlighted that there is not one type of training that can be recommended to best improve RSA and all of the factors believed to be responsible for performance decrements during repeated-sprint tasks. This is not surprising, as RSA is a complex fitness component that depends on both metabolic (e.g. oxidative capacity, phosphocreatine recovery and H+ buffering) and neural factors (e.g. muscle activation and recruitment strategies) among others. While different training strategies can be used in order to improve each of these potential limiting factors, and in turn RSA, two key recommendations emerge from this review; it is important to include (i) some training to improve single-sprint performance (e.g. 'traditional' sprint training and strength/power training); and (ii) some high-intensity (80-90% maximal oxygen consumption) interval training to best improve the ability to recover between sprints. Further research is required to establish whether it is best to develop these qualities separately, or whether they can be developed concurrently (without interference effects). While research has identified a correlation between RSA and total sprint distance during soccer, future studies need to address whether training-induced changes in RSA also produce changes in match physical performance.

Similar changes of gene expression in human skeletal muscle after resistance exercise and multiple fine needle biopsies

Repeated biopsy sampling from one muscle is necessary to investigate muscular adaptation to different forms of exercise as adaptation is thought to be the result of cumulative effects of transient changes in gene expression in response to single exercise bouts. In a crossover study, we obtained four fine needle biopsies from one vastus lateralis muscle of 11 male subjects (25.9 ± 3.8 yr, 179.2 ± 4.8 cm, 76.5 ± 7.0 kg), taken before (baseline), 1, 4, and 24 h after one bout of squatting exercise performed as conventional squatting or as whole body vibration exercise. To investigate if the repeated biopsy sampling has a confounding effect on the observed changes in gene expression, four fine needle biopsies from one vastus lateralis muscle were also taken from 8 male nonexercising control subjects (24.5 ± 3.7 yr, 180.6 ± 1.2 cm, 81.2 ± 1.6 kg) at the equivalent time points. Using RT-PCR, we observed similar patterns of change in the squatting as well as in the control group for the mRNAs of interleukin 6 (IL-6), IL-6 receptor, insulin-like growth factor 1, p21, phosphofructokinase, and glucose transporter in relation to the baseline biopsy. In conclusion, multiple fine needle biopsies obtained from the same muscle region can per se influence the expression of marker genes induced by an acute bout of resistance exercise.

Rapid aminoacidemia enhances myofibrillar protein synthesis and anabolic intramuscular signaling responses after resistance exercise

BACKGROUND

Ingestion of whey or casein yields divergent patterns of aminoacidemia that influence whole-body and skeletal muscle myofibrillar protein synthesis (MPS) after exercise. Direct comparisons of the effects of contrasting absorption rates exhibited by these proteins are confounded by their differing amino acid contents.

OBJECTIVE

Our objective was to determine the effect of divergent aminoacidemia by manipulating ingestion patterns of whey protein alone on MPS and anabolic signaling after resistance exercise.

DESIGN

In separate trials, 8 healthy men consumed whey protein either as a single bolus (BOLUS; 25-g dose) or as repeated, small, "pulsed" drinks (PULSE; ten 2.5-g drinks every 20 min) to mimic a more slowly digested protein. MPS and phosphorylation of signaling proteins involved in protein synthesis were measured at rest and after resistance exercise.

RESULTS

BOLUS increased blood essential amino acid (EAA) concentrations above those of PULSE (162% compared with 53%, P < 0.001) 60 min after exercise, whereas PULSE resulted in a smaller but sustained increase in aminoacidemia that remained elevated above BOLUS amounts later (180-220 min after exercise, P < 0.05). Despite an identical net area under the EAA curve, MPS was elevated to a greater extent after BOLUS than after PULSE early (1-3 h: 95% compared with 42%) and later (3-5 h: 193% compared with 121%) (both P < 0.05). There were greater changes in the phosphorylation of the Akt-mammalian target of rapamycin pathway after BOLUS than after PULSE.

CONCLUSIONS

Rapid aminoacidemia in the postexercise period enhances MPS and anabolic signaling to a greater extent than an identical amount of protein fed in small pulses that mimic a more slowly digested protein. A pronounced peak aminoacidemia after exercise enhances protein synthesis. This trial was registered at clinicaltrials.gov as NCT01319513.

Strategies to optimize concurrent training of strength and aerobic fitness for rowing and canoeing

During the last several decades many researchers have reported an interference effect on muscle strength development when strength and endurance were trained concurrently. The majority of these studies found that the magnitude of increase in maximum strength was higher in the group that performed only strength training compared with the concurrent training group, commonly referred to as the 'interference phenomenon'. Currently, concurrent strength and endurance training has become essential to optimizing athletic performance in middle- and long-distance events. Rowing and canoeing, especially in the case of Olympic events, with exercise efforts between 30 seconds and 8 minutes, require high amounts of maximal aerobic and anaerobic capacities as well as high levels of maximum strength and muscle power. Thus, strength training, in events such as rowing and canoeing, is integrated into the training plan. However, several studies indicate that the degree of interference is affected by the training protocols and there may be ways in which the interference effect can be minimized or avoided. Therefore, the aim of this review is to recommend strategies, based on research, to avoid or minimize any interference effect when training to optimize performance in endurance sports such as rowing and canoeing.

Early time course of Akt phosphorylation after endurance and resistance exercise

PURPOSE

The aim of this study was to determine the early time course of exercise-induced signaling after divergent contractile activity associated with resistance and endurance exercise.

METHODS

Sixteen male subjects were randomly assigned to either a cycling (CYC; n = 8, 60 min, 70% V˙O2peak) or resistance (REX; n = 8, 8 x 5 leg extension, 80% one-repetition maximum, 3-min recovery) exercise group. Serial muscle biopsies were obtained from vastus lateralis at rest before, immediately after, and after 15, 30, and 60 min of passive recovery to determine early signaling responses after exercise.

RESULTS

There were comparable increases from rest in Akt(Thr308/Ser473) and mTOR(Ser2448) phosphorylation during the postexercise time course that peaked 30-60 min after both CYC and REX (P < 0.05). There were also similar patterns in p70S6K(Thr389) and 4E-BP1(Thr37/46) phosphorylation, but a greater magnitude of effect was observed for REX and CYC, respectively (P < 0.05). However, AMPK(Thr172) phosphorylation was only significantly elevated after CYC (P < 0.05), and we observed divergent responses for glycogen synthase(Ser641) and AS160 phosphorylation that were enhanced after CYC but not REX (P < 0.05).

CONCLUSIONS

We show a similar time course for Akt-mTOR-S6K phosphorylation during the initial 60-min recovery period after divergent contractile stimuli. Conversely, enhanced phosphorylation status of proteins that promote glucose transport and glycogen synthesis only occurred after endurance exercise. Our results indicate that endurance and resistance exercise initiate translational signaling, but high-load, low-repetition contractile activity failed to promote phosphorylation of pathways regulating glucose metabolism.

Nutrient provision increases signalling and protein synthesis in human skeletal muscle after repeated sprints

The effect of nutrient availability on the acute molecular responses following repeated sprint exercise is unknown. The aim of this study was to determine skeletal muscle cellular and protein synthetic responses following repeated sprint exercise with nutrient provision. Eight healthy young male subjects undertook two sprint cycling sessions (10 × 6 s, 0.75 N m torque kg(-1), 54 s recovery) with either pre-exercise nutrient (24 g whey, 4.8 g leucine, 50 g maltodextrin) or non-caloric placebo ingestion. Muscle biopsies were taken from vastus lateralis at rest, and after 15 and 240 min post-exercise recovery to determine muscle cell signalling responses and protein synthesis by primed constant infusion of L: -[ring-(13)C(6)] phenylalanine. Peak and mean power outputs were similar between nutrient and placebo trials. Post-exercise myofibrillar protein synthetic rate was greater with nutrient ingestion compared with placebo (~48%, P < 0.05) but the rate of mitochondrial protein synthesis was similar between treatments. The increased myofibrillar protein synthesis following sprints with nutrient ingestion was associated with coordinated increases in Akt-mTOR-S6K-rpS6 phosphorylation 15 min post-exercise (~200-600%, P < 0.05), while there was no effect on these signalling molecules when exercise was undertaken in the fasted state. For the first time we report a beneficial effect of nutrient provision on anabolic signalling and muscle myofibrillar protein synthesis following repeated sprint exercise. Ingestion of protein/carbohydrate in close proximity to high-intensity sprint exercise provides an environment that increases cell signalling and protein synthesis.