Transcranial Direct Current Stimulation over the Left Dorsolateral Prefrontal Cortex Improves Inhibitory Control and Endurance Performance in Healthy Individuals.

The dorsolateral prefrontal cortex (DLPFC) is a crucial brain region for inhibitory control, an executive function essential for behavioral self-regulation. Recently, inhibitory control has been shown to be important for endurance performance. Improvement in inhibitory control was found following transcranial direct current stimulation (tDCS) applied over the left DLPFC (L-DLPFC). This study examined the effect tDCS on both an inhibitory control and endurance performance in a group of healthy individuals. Twelve participants received either real tDCS (Real-tDCS) or placebo tDCS (Sham-tDCS) in randomized order. The anodal electrode was placed over the L-DLPFC while the cathodal electrode was placed above Fp2. Stimulation lasted 30min with current intensity set at 2mA. A Stroop test was administered to assess inhibitory control. Heart rate (HR), ratings of perceived exertion (RPE), and leg muscle pain (PAIN) were monitored during the cycling time to exhaustion (TTE) test, while blood lactate accumulation (∆B[La-]) was measured at exhaustion. Stroop task performance was improved after Real-tDCS as demonstrated by a lower number of errors for incongruent stimuli (p=0.012). TTE was significantly longer following Real-tDCS compared to Sham-tDCS (p=0.029, 17±8 vs 15±8min), with significantly lower HR (p=0.002) and RPE (p<0.001), while no significant difference was found for PAIN (p>0.224). ∆B[La-] was significantly higher at exhaustion in Real-tDCS (p=0.040). Our findings provide preliminary evidence that tDCS with the anodal electrode over the L-DLPFC can improve both inhibitory control and endurance cycling performance in healthy individuals.

Effects of caffeine on reaction time are mediated by attentional rather than motor processes.

BACKGROUND: Caffeine has a well-established effect on reaction times (RTs) but the neurocognitive mechanisms underlying this are unclear. METHODS: In the present study, 15 female participants performed an oddball task after ingesting caffeine or a placebo, and electroencephalographic data were obtained. Single-trial P3b latencies locked to the stimulus and to the response were extracted and mediation models were fitted to the data to test whether caffeine's effect on RTs was mediated by its effect on either type of P3b latencies. RESULTS: Stimulus-locked latencies showed clear evidence of mediation, with approximately a third of the effect of caffeine on RTs running through the processes measured by stimulus-locked latencies. Caffeine did not affect response-locked latencies, so could not mediate the effect. DISCUSSION: These findings are consistent with caffeine's effect on RTs being a result of its effect on perceptual-attentional processes, rather than motor processes. The study is the first to apply mediation analysis to single-trial P3b data and this technique holds promise for mental chronometric studies into the effects of psychopharmacological agents. The R code for performing the single trial analysis and mediation analysis are included as supplementary materials.

Bilateral extracephalic transcranial direct current stimulation improves endurance performance in healthy individuals.

BACKGROUND: Transcranial direct current stimulation (tDCS) has been used to enhance endurance performance but its precise mechanisms and effects remain unknown. OBJECTIVE: To investigate the effect of bilateral tDCS on neuromuscular function and performance during a cycling time to task failure (TTF) test. METHODS: Twelve participants in randomized order received a placebo tDCS (SHAM) or real tDCS with two cathodes (CATHODAL) or two anodes (ANODAL) over bilateral motor cortices and the opposite electrode pair over the ipsilateral shoulders. Each session lasted 10 min and current was set at 2 mA. Neuromuscular assessment was performed before and after tDCS and was followed by a cycling time to task failure (TTF) test. Heart rate (HR), ratings of perceived exertion (RPE), leg muscle pain (PAIN) and blood lactate accumulation (ΔB[La-]) in response to the cycling TTF test were measured. RESULTS: Corticospinal excitability increased in the ANODAL condition (P < 0.001) while none of the other neuromuscular parameters showed any change. Neuromuscular parameters did not change in the SHAM and CATHODAL conditions. TTF was significantly longer in the ANODAL (P = 0.003) compared to CATHODAL and SHAM conditions (12.61 ± 4.65 min; 10.61 ± 4.34 min; 10.21 ± 3.47 min respectively), with significantly lower RPE and higher ΔB[La-] (P < 0.001). No differences between conditions were found for HR (P = 0.803) and PAIN during the cycling TTF test (P = 0.305). CONCLUSION: Our findings demonstrate that tDCS with the anode over both motor cortices using a bilateral extracephalic reference improves endurance performance.

Effect of a Mediterranean Type Diet on Inflammatory and Cartilage Degradation Biomarkers in Patients with Osteoarthritis.

OBJECTIVES: To investigate the effects of a Mediterranean type diet on patients with osteoarthritis (OA). PARTICIPANTS: Ninety-nine volunteers with OA (aged 31 - 90 years) completed the study (83% female). SETTING: Southeast of England, UK. DESIGN: Participants were randomly allocated to the dietary intervention (DIET, n = 50) or control (CON, n = 49). The DIET group were asked to follow a Mediterranean type diet for 16 weeks whereas the CON group were asked to follow their normal diet. MEASUREMENTS: All participants completed an Arthritis Impact Measurement Scale (AIMS2) pre-, mid- and post- study period. A subset of participants attended a clinic at the start and end of the study for assessment of joint range of motion, ROM (DIET = 33, CON = 28), and to provide blood samples (DIET = 29, CON = 25) for biomarker analysis (including serum cartilage oligomeric matrix protein (sCOMP) (a marker of cartilage degradation) and a panel of other relevant biomarkers including pro- and anti-inflammatory cytokines). RESULTS: There were no differences between groups in the response of any AIMS2 components and most biomarkers (p > 0.05), except the pro-inflammatory cytokine IL-1α, which decreased in the DIET group (~47%, p = 0.010). sCOMP decreased in the DIET group by 1 U/L (~8%, p = 0.014). There was a significant improvement in knee flexion and hip rotation ROM in the DIET group (p < 0.05). CONCLUSIONS: The average reduction in sCOMP in the DIET group (1 U/L) represents a meaningful change, but the longer term effects require further study.

Transcranial direct current stimulation improves isometric time to exhaustion of the knee extensors.

Transcranial direct current stimulation (tDCS) can increase cortical excitability of a targeted brain area, which may affect endurance exercise performance. However, optimal electrode placement for tDCS remains unclear. We tested the effect of two different tDCS electrode montages for improving exercise performance. Nine subjects underwent a control (CON), placebo (SHAM) and two different tDCS montage sessions in a randomized design. In one tDCS session, the anodal electrode was placed over the left motor cortex and the cathodal on contralateral forehead (HEAD), while for the other montage the anodal electrode was placed over the left motor cortex and cathodal electrode above the shoulder (SHOULDER). tDCS was delivered for 10min at 2.0mA, after which participants performed an isometric time to exhaustion (TTE) test of the right knee extensors. Peripheral and central neuromuscular parameters were assessed at baseline, after tDCS application and after TTE. Heart rate (HR), ratings of perceived exertion (RPE), and leg muscle exercise-induced muscle pain (PAIN) were monitored during the TTE. TTE was longer and RPE lower in the SHOULDER condition (P<0.05). Central and peripheral parameters, and HR and PAIN did not present any differences between conditions after tDCS stimulation (P>0.05). In all conditions maximal voluntary contraction (MVC) significantly decreased after the TTE (P<0.05) while motor-evoked potential area (MEP) increased after TTE (P<0.05). These findings demonstrate that SHOULDER montage is more effective than HEAD montage to improve endurance performance, likely through avoiding the negative effects of the cathode on excitability.

Effect of exercise-induced muscle damage on endurance running performance in humans.

Exercise-induced muscle damage (EIMD) is known to decrease muscle strength and power but its effect on endurance performance is unclear. Thirty moderately trained adult runners (24 men and six women) were randomly assigned to EIMD or control. The EIMD group jumped 100 times from a 35 cm bench, while controls did not perform any muscle-damaging exercise. Before and 48 h after treatment, subjects were tested on markers of EIMD, steady-state cardiorespiratory, metabolic and perceptual responses during a constant speed submaximal run; distance ran in 30 min on a treadmill. There were significant changes in muscle soreness, creatine kinase, and knee extensors strength (P<0.01). This EIMD significantly reduced self-paced time trial performance by 4% (P<0.01) because subjects reduced running speed (P=0.02), with no change in perceived exertion (P=0.31). No significant alterations in running economy and other physiological responses to submaximal running were found. However, there was a trend (P=0.08) for increased perceived exertion, which was correlated with decreased time trial performance (P<0.01). In conclusion, EIMD has a significant impact on endurance running performance in humans, and this effect seems to be mediated by alterations in the sense of effort.

Validity of simple field tests as indicators of match-related physical performance in top-level professional soccer players.

The aim of this study was to examine the construct validity of selected field tests as indicators of match-related physical performance. During the competitive season, eighteen professional soccer players (age 26.2 +/- 4.5 yrs, mass 80.8 +/- 7.8 kg, and height 181.9 +/- 3.7 cm) completed an incremental running field test to exhaustion, a vertical-jump and a repeated-sprint ability (RSA) test. Match physical performance was quantified during official matches using a video-computerized, semi-automatic, match analysis image recognition system, (ProZone, Leeds, UK). The selected measures of match physical performance were: total distance covered (TD), high intensity running (HIR: > 14.4 km . h (-1)), very high intensity running (VHIR:> 19.8 km . h (-1)), sprinting (> 25.2 km . h (-1)) and top running speed. Significant correlations were found between peak speed reached during the incremental field test and TD (r = 0.58, R (2) = 0.34; p < 0.05), HIR (r = 0.65, R (2) = 0.42; p < 0.01) and VHIR (r = 0.64, R (2) = 0.41; p < 0.01). Significant correlations were also found between RSA mean time and VHIR (r = - 0.60, R (2) = 0.36; p < 0.01) and sprinting distance (r = - 0.65, R (2) = 0.42; p < 0.01). Significant differences were found between the best and worst group as defined by the median split technique for peak speed (TD = 12 011 +/- 747 m vs. 10 712 +/- 669, HIR = 3192 +/- 482 m vs. 2314 +/- 347 m, and VHIR = 1014 +/- 120 vs. 779 +/- 122 m, respectively; p < 0.05) and RSA mean time (VHIR = 974 +/- 162 m vs. 819 +/- 144 m, and sprinting = 235 +/- 56 vs. 164 +/- 58 m, respectively; p < 0.05). In conclusion, this study gives empirical support to the construct validity of RSA and incremental running tests as measures of match-related physical performance in top-level professional soccer players.

Physiological and performance effects of generic versus specific aerobic training in soccer players.

The aim of this study was to compare the effects of specific (small-sided games) vs. generic (running) aerobic interval training on physical fitness and objective measures of match performance in soccer. Forty junior players were randomly assigned to either generic (n=20) or specific (n=20) interval training consisting of 4 bouts of 4 min at 90-95 % of maximum heart rate with 3 min active rest periods, completed twice a week. The following outcomes were measured at baseline (Pre), after 4 weeks of pre-season training (Mid), and after a further 8 weeks of training during the regular season (Post): maximum oxygen uptake, lactate threshold (Tlac), running economy at Tlac, a soccer-specific endurance test (Ekblom's circuit), and indices of physical performance during soccer matches (total distance and time spent standing, walking, and at low- and high-intensity running speed). Training load, as quantified by heart rate and rating of perceived exertion, was recorded during all training sessions and was similar between groups. There were significant improvements in aerobic fitness and match performance in both groups of soccer players, especially in response to the first 4 weeks of pre-season training. However, no significant differences between specific and generic aerobic interval training were found in any of the measured variables including soccer specific tests. The results of this study showed that both small-sided games and running are equally effective modes of aerobic interval training in junior soccer players.

Prediction of time to exhaustion from blood lactate response during submaximal exercise in competitive cyclists.

The aim of this investigation was to develop and validate a new method to predict time to exhaustion (pTE) from blood lactate variables measured during a submaximal non-exhaustive constant workload cycling test in professional cyclists. A multiple regression equation to estimate pTE from blood lactate variables measured within the first 10 min of a submaximal test and TE was determined in 40 competitive cyclists. Predicted TE reliability [individual coefficient of variation (CV)] was calculated in eight amateur cyclists who repeated the proposed test three times. Seasonal variations of pTE were monitored in 12 professional cyclists. Validity of pTE was determined by the known-group difference method in 49 professional cyclists. The prediction equation was: log(n)TE = 4.2067 - 0.8221(log(n) B) - 0.2519(log(n) C), where B is the lactate concentration at the 10th minute of the constant workload test and C is the lactate slope calculated between the 5th and 10th minute (adjusted r (2) =0.83, root mean square error in cross validation=23.1%). Predicted TE CV was 11.7%. The pTE obtained at the beginning of the season and the best and worst tests performed during the competitive season, resulted 162, 224 and 103% higher than the basic period test, respectively (P<0.05). Predicted TE was the only parameter discriminating elite from subelite professional cyclists. In conclusion, this study demonstrates that pTE is a valid and practical alternative to incremental tests and direct measures of endurance capacity requiring exhaustive efforts for the evaluation of competitive cyclists.

Cardiovascular responses to aerobic step dance sessions with and without appendicular overload.

AIM: Several studies showed that exercise intensity during aerobic step dance can be modified varying stepping rate, bench height and manipulating body mass using hand held or adding loads to the torso. The aim of this study was to determine the cardiovascular responses during aerobic step dance using an overload strategy not yet investigated: appendicular overload. METHODS: Ten healthy and moderately trained women (mean+/-SD: age 27+/-3.4 years, height 167.8+/-4.6 cm, body mass 55.7+/-4.7 kg, body mass index 19.8+/-1.6, VO2max44.4+/-6.1 mLxkg-1xmin-1) performed an incremental treadmill test to determine VO2peak, the VO2-heart rate (HR) and rating of perceived exertion (RPE)-HR relationships. Within 1 week from the laboratory test, the subjects performed two identical aerobic step dance routines: one using a track suit with loads placed in pockets close to the legs and arms and another without overload. RESULTS: The appendicular overload (10% of body mass) significantly increased the exercise intensity from 84.5% to 89.8% of HRmax corresponding to 68.9% and 78.3% of VO2peak, respectively (P<0.01). Similarly, RPE increased from 12.1 to 15.7 (P<0.001). The estimated VO2 and the caloric expenditure rose from 30.3 to 34.7 mLxkg-1xmin-1 and from 251 to 288 kcal, respectively. CONCLUSION: This study shows that the use of appendicular overload significantly increases the energy cost of aerobic step session similarly to other overload strategies already reported in the literature.

Correlations between physiological variables and performance in high level cross country off road cyclists.

OBJECTIVES: To examine the relations between maximal and submaximal indices of aerobic fitness and off road cycling performance in a homogeneous group of high level mountain bikers. METHODS: 12 internationally competitive mountain bikers completed the study. Maximum oxygen uptake (Vo(2max)), peak power output (PPO), power output (PO), and oxygen uptake (Vo(2)) at first (VT) and second (RCT) ventilatory thresholds were measured in the laboratory, and correlated with race time during a cross country circuit race. RESULTS: The only physiological indices of aerobic fitness correlated with off road cycling performance were PO and Vo(2) at RCT when normalised to body mass (r = -0.63 and r = -0.66, respectively; p<0.05). VT, Vo(2max), and PPO were not correlated to performance in this homogeneous group of high level mountain bikers. CONCLUSIONS: The results of this study suggest that submaximal indices of aerobic fitness such as PO and Vo(2) at RCT are more important determinants of off road cycling performance than maximal indices such as PPO and Vo(2max). This study confirms the importance of body mass for mountain biking performance. As aerobic fitness explained only 40% of the variance, other physiological and technical factors should be investigated, as they may be important determinants of cross country performance among elite mountain bikers.