Concurrent brain endurance training improves endurance exercise performance

ObjectivesMental fatigue impairs endurance exercise. Brain endurance training (BET) – engaging in cognitively fatiguing tasks during exercise - can develop resilience to mental fatigue and improve physical performance over physical training alone. The mechanism for this effect is unknown.This experiment examines if BET enhances performance over physical training and investigates potential underlying physiological mechanisms.DesignA mixed design randomised control trial.MethodsPre- and post-testing: 36 participants completed dynamic rhythmic muscular endurance handgrip tasks requiring generation of as much force as possible once a second for 300 s, performed under 3 counterbalanced conditions: following 600 s of a 2-back memory/attention task (subsequent); while performing a 2-back task (concurrent); and on its own (solo). Cardiac activity, electromyographic forearm activity, pre-frontal cerebral haemodynamics (near infrared spectroscopy), and force were recorded. Training: Participants (randomised to a Control or BET group) completed 24 (6 weeks) submaximal hand contractions sessions. The BET group also completed concurrent cognitive tasks (2-back, Stroop). Measures of motivation, physical and mental exertion and mental fatigue were collected throughout.ResultsEndurance performance, across the 3 tasks, improved more following BET (32%) than Control (12%) (p < 0.05). The better performance following BET occurred with a higher pre-frontal oxygenation during the post-training physical tasks over time relative to Control (p < 0.05).ConclusionsConcurrent BET improved endurance performance over physical training alone. This was accompanied by a training-induced maintenance of pre-frontal oxygenation, suggestive of reduced mental effort during physical activity.     

Trunk endurance,posterior chain flexibility,and previous history of musculoskeletal pain predict overuse low back and lower extremity injury: a prospective cohort study of 545 Navy Cadets

ObjectiveTo investigate predictors of low back and lower extremity musculoskeletal injury in a cohort of Naval cadets.DesignProspective Cohort StudyMethods545 Naval cadets (Males, n = 394, 72%) were followed-up over eight months. Nine variables were investigated as predictors: history of musculoskeletal symptoms in the last 12 months, ankle dorsiflexion range of motion, sit and reach test, isometric hip abduction and external rotation strength, alignment during the single leg squat test, single leg hop test for distance, prone plank and side plank tests. All injuries that required medical attention were registered. Predictive associations were examined using univariable and multivariable logistic regression analyses.ResultsThe incidence of all injuries was 7%. Cadets who failed the 60-second plank test (OR = 3.3; 95% CI, 1.2?8.8, P = 0.04), had ≤18 cm in the sit and reach test (OR = 4.0; 95% CI, 1.4?11.2, P = 0.01), or reported pain in the last 12 months in two or more body regions (OR = 2.7; 95% CI, 1.02?7.3, P = 0.04), had greater odds of sustaining an overuse injury. No predictors were identified for acute injuries.ConclusionDecreased trunk endurance on the prone plank test, reduced posterior chain flexibility on the sit and reach test, and a history of pain reported in two or more sites in the last 12 months were predictors of overuse injuries in Naval cadets. Assessment and intervention of these modifiable risk factors may be clinically relevant in injury screening and prevention.     

Strength/endurance training versus endurance training in congestive heart failure

PURPOSE: The aim of this study was to compare the effects of endurance training alone (ET) with combined endurance and strength training (CT) on hemodynamic and strength parameters in patients with congestive heart failure (CHF). METHODS: Twenty male patients with CHF were randomized into one of two training regimens consisting of endurance training or a combination of endurance and resistance training. Group ET had 40-min interval cycle ergometer endurance training three times per week. Group CT combined endurance and strength training with the same interval endurance training for 20 min, followed by 20 min of strength training. Left ventricular function was assessed at baseline and after 40 training sessions by echocardiography and radionuclide ventriculography. Work capacity was measured with cardiopulmonary exercise test (CPX) and lactate determination. Strength was measured with an isokinetic dynamometer. RESULTS: After 40 sessions, the ET group improved functional class, work capacity, peak torque, and muscular endurance. However, peak O2 remained unchanged. Left ventricular ejection fraction (LVEF) and fractional shortening (FS) decreased, whereas left ventricular end-diastolic diameter (LVED) increased. The CT group improved NYHA score, working capacity, peak O2, and peak lactate; peak torque and muscular endurance, LVEF, and FS increased, whereas LVED decreased. Compared with ET, CT was significantly (P < 0.05) better in improving LV function.CONCLUSION: Combined endurance/strength training was superior to endurance training alone concerning improvement of LV function, peak VO2, and strength parameters. It appears that for stable CHF patients, a greater benefit can be derived from this training modality.     

Pregnancy in endurance athletes

The purpose of the present study was to examine pregnancy and delivery among Finnish endurance athletes at the national top level. A questionnaire concerning first. pregnancy was sent to 30 Finnish endurance athletes who had been at national top level in cross-country skiing, running, speed-skating or orienteering. Data on labour were collected retrospectively through a questionnaire and from the diaries in the hospital concerned. The next primipara in the diaries formed a member of the control group. Twenty-three athletes (77%) had regular menstrual cycles, seven (23%) had irregularities, and four of them had received hormonal treatment for this. Seven athletes (23%) had experienced spontaneous abortion during the first trimester in previous pregnancy. Sixteen (53%) did not notice any change in their exercise performance, three (10%) subjectively felt themselves to be in a better physical condition, and seven (23%) felt themselves to be in a worse condition than before the pregnancy. Four did not respond on the question. After delivery, 18 athletes continued to compete, the median interval being 8.2 months (range 2–24 months). Two of them (11%) achieved a better condition than before the pregnancy, 11 (61%) reached the same level and five (28%) did not achieve the same performance level. There were no significant differences in labour parameters between the athletes and controls. Endurance training had no harmful side-effects on the pregnancies or deliveries of the athletes. The effect of pregnancy on exercise performance is individual.     

Caffeine and endurance performance

The belief among athletes that caffeine is an ergogenic aid is common, and several governing bodies of sport have barred use of the drug during competition. At the cellular level, caffeine has been implicated to affect the translocation of calcium in muscle, promote an increase in cellular levels of cyclic AMP and cause a blockade of adenosine receptors in the central nervous system. The general systemic effect of caffeine is to cause central nervous system arousal, mobilisation of free fatty acids and other metabolites, and possibly enhance the contractile status of muscle. At present, the scientific community remains divided as to whether caffeine ingestion will indeed produce an ergogenic effect upon sport performance. Some evidence suggests that caffeine may improve performance in events relying upon strength and power; however, the lack of in vivo research in humans makes it difficult to form firm conclusions. In addition, reports concerning caffeine's effect on VO2max and performance during incremental exercise are not in agreement. On the other hand, recent studies suggest that caffeine might indeed have ergogenic potential in endurance events (e.g. marathon running). It is hypothesised that the mechanism behind these findings is related to the increased availability of free fatty acids for muscle metabolism which has a glycogen-sparing effect.     

Effects of submaximal and supramaximal interval training on determinants of endurance performance in endurance athletes

We compared the effects of submaximal and supramaximal cycling interval training on determinants of exercise performance in moderately endurance‐trained men. Maximal oxygen consumption (VO_2max), peak power output (P_peak), and peak and mean anaerobic power were measured before and after 6 weeks (3 sessions/week) of submaximal (85% maximal aerobic power [MP], HIIT₈₅, n = 8) or supramaximal (115% MP, HIIT₁₁₅, n = 9) interval training to exhaustion in moderately endurance‐trained men. High‐intensity training volume was 47% lower in HIIT₁₁₅ vs HIIT₈₅ (304 ± 77 vs 571 ± 200 min; P < 0.01). Exercise training was generally associated with increased VO_2max (HIIT₈₅: +3.3 ± 3.1 mL/kg/min; HIIT₁₁₅: +3.3 ± 3.6 ml/kg/min; Time effect P = 0.002; Group effect: P = 0.95), P_peak (HIIT₈₅: +18 ± 9 W; HIIT₁₁₅: +16 ± 27 W; Time effect P = 0.045; Group effect: P = 0.49), and mean anaerobic power (HIIT₈₅: +0.42 ± 0.69 W/kg; HIIT₁₁₅: +0.55 ± 0.65 W/kg; Time effect P = 0.01; Group effect: P = 0.18). Six weeks of submaximal and supramaximal interval training performed to exhaustion seems to equally improve VO_2max and anaerobic power in endurance‐trained men, despite half the accumulated time spent at the target intensity.     

Effects of respiratory muscle endurance training on ventilatory and endurance performance of moderately trained cyclists

This study examined the effects of respiratory muscle endurance training (RMET) on ventilatory and endurance performance among moderately trained, male cyclists. Nine subjects initially completed two cycling VO2 max tests, two endurance cycling tests for time at 95% VO2 max, a 15-s MVV test, and an endurance breathing test for time at 100% MVV. Four subjects then underwent 3 weeks of strenuous RMET while five served as controls. Mean posttest 15-s MVV and endurance breathing time were significantly higher in the RMET group (243 +/- 14 l X min-1 and 804 +/- 94 s) than in the control group (205 +/- 6 l X min-1 and 48 +/- 8 s). No significant group differences in VO2 max or endurance cycling time at 95% VO2 max were observed following RMET. Results of this exploratory study indicated that RMET improved ventilatory power and endurance, but did not alter VO2 max or endurance cycling performance among moderately trained, male cyclists.     

Heart rate variability in prediction of individual adaptation to endurance training in recreational endurance runners

The aim of this study was to investigate whether nocturnal heart rate variability (HRV) can be used to predict changes in endurance performance during 28 weeks of endurance training. The training was divided into 14 weeks of basic training (BTP) and 14 weeks of intensive training periods (ITP). Endurance performance characteristics, nocturnal HRV, and serum hormone concentrations were measured before and after both training periods in 28 recreational endurance runners. During the study peak treadmill running speed (V_peak) improved by 7.5±4.5%. No changes were observed in HRV indices after BTP, but after ITP, these indices increased significantly (HFP: 1.9%, P=0.026; TP: 1.7%, P=0.007). Significant correlations were observed between the change of V_peak and HRV indices (TP: r=0.75, P<0.001; HFP: r=0.71, P<0.001; LFP: r=0.69, P=0.01) at baseline during ITP. In order to lead to significant changes in HRV among recreational endurance runners, it seems that moderate‐ and high‐intensity training are needed. This study showed that recreational endurance runners with a high HRV at baseline improved their endurance running performance after ITP more than runners with low baseline HRV.     

Sperm characteristics of endurance trained cyclists

The purpose of this study was to investigate the influence of cycling on sperm characteristics. Twenty subjects volunteered for the study, comprising 10 long distance competitive cyclists (median 25.5 y) and 10 sedentary controls (median 24.5 y). A questionnaire was used to obtain a history of training, health, nutrition and life style. Semen analysis consisted of a detailed evaluation of sperm characteristics that included semen volume, sperm count, viability, motility and morphology. Compared to controls, the cyclists had a significantly lower proportion of spermatozoa with normal morphology (medians: 41.5 % versus 19.5 %; p < 0.01) and a significantly higher proportion of morphologically abnormal tapered forms (medians: 4.5 % versus 22.5 %; p < 0.01). No significant difference in semen volume and sperm motility, viability and count was observed between the two groups. We concluded that endurance cycling appears to be associated with a significant alteration in sperm morphology.     

Physiological determinants of endurance exercise performance

Performance in endurance events is typically evaluated by the power or velocity that can be maintained for durations of 30 min. to four hours. The two main by-products of intense and prolonged oxidative metabolism that can limit performance are the accumulation of hydrogen ion (i.e. lactic acidosis) and heat (i.e. hyperthermia). A model for endurance performance is presented that revolves around identification of the lactate threshold velocity which is presented as a function of numerous morphological components as well as gross mechanical efficiency. When cycling at 80 RPM, gross mechanical efficiency is positively related to Type I muscle fiber composition, which has great potential to improve endurance performance. Endurance performance can also be influenced by altering the availability of oxygen and blood glucose during exercise. The latter need forms the basis for ingesting carbohydrate at 30-60 grams per hour during exercise. In laboratory simulations of performance, athletes fatigue due to hyperthermia when esophageal is approximately 40 degrees C, in association with near maximal heart rate and perceived exertion. It is likely that the central nervous system is involved in the aetiology of fatigue from hyperthermia. Dehydration during exercise promotes hyperthermia by reducing skin blood flow, sweating rate and thus heat dissipation. The combination of dehydration and hyperthermia during exercise causes large reductions in cardiac output and blood flow to the exercising musculature, and thus has a large potential to impair endurance performance. Endurance performance is optimized when training is aimed specifically at developing individual components of the model presented and nutritional supplementation prevents hypoglycemia and attenuates dehydration and hyperthermia. Indeed, the challenge at the transition to a new millennium is to synergistically integrate these physiological factors in training and competition.     

Asymptomatic bradycardia amongst endurance athletes

It is established that an intensive training results in a lower average resting heart rate. Management of bradycardia in an athlete can be difficult given the underlying mechanisms are not clearly understood. The authors reviewed the different mechanisms described in the literature, including recent advances in physiology regarding remodeling of ion channels, which may partially explain bradycardia in athletes. Sinus bradycardia amongst athletes, especially endurance focused athletes, is common but difficult to apprehend. The underlying mechanisms are observably of multifactorial origin and likely incompletely elucidated by the current body of knowledge.     

Gastrointestinal symptoms during endurance running

The incidence and type of gastrointestinal complaints among endurance runners were investigated with a questionnaire among participants in a marathon event in northern Finland. The running distances were 1/4, 1/2 and full marathon. The fitness level of the participants varied from habitual joggers to national-class endurance runners. The response rate of the 426 participants was 55% (230). Gastrointestinal disturbances during the run were reported by 32% of the respondents. The prominent symptom during the 1/4 marathon was stitch (32%). The main complaints during the 1/2 marathon were stitch (21%), pain (12%), and retching or heartburn (5%). The most frequent symptoms during the full marathon were stitch (16%), pain (9%), diarrhoea (4%) and nausea (4%). Gastrointestinal symptoms hindered maximal performance subjectively for 16%, 18% and 19% in the 1/4, 1/2 and full marathon, respectively. Most of the symptomatic runners (73%) had suffered from gastrointestinal complaints during the preceding training period, and 25% of the asymptomatic runners reported previous gastrointestinal troubles during training.     

Muscle damage and endurance events

Intensive training for and competition in endurance events like the marathon are accompanied by injury to fibres in the active skeletal muscles. Evidence for the injury comes from the increases in intramuscular enzymes and myoglobin found in the blood following the exercise, from the subjective sensation of soreness in the muscles in the post-exercise period, and from direct histological examination of samples of the damaged muscles. Histological studies demonstrate that some muscle fibres undergo degenerative changes following the exercise; the necrosis is accomplished by macrophages and other phagocytic cells that invade the injured cells and the adjacent interstitium. Following the degeneration the fibers appear to be regenerated so that there is not a net loss of fibres. Precisely what initiates the cellular damage is not known, but hypotheses suggested include, 'metabolic overload' and 'mechanical strain'. Eccentric contractions are known to cause the greater amount of damage in muscles, which suggests that high local tensions in fibres may be more important than metabolic considerations in the aetiology of the injury. Training reduces the magnitude of the damage that occurs in response to a given exercise task, although competitors in endurance events may demonstrate chronic muscle injury because of increasing training intensities. Other than training, there is no compelling evidence that any drug treatment or preventative measures will lessen this form of injury.