Effects of Transcranial Direct Current Stimulation on Endurance Performance of Lower Limbs:A Systematic Review / 医用生物力学

Sports fatigue of the lower limbs is one of the important factors affecting sports performance. How to improve the anti-fatigue ability of the lower limbs during endurance exercise is the focus of the research field of human sports biomechanics. This study systematically reviewed the relevant literature on transcranial direct current stimulation (tDCS) intervention on lower limb endurance performance, summarized the effect of tDCS on lower limb endurance performance, and analyzed the influencing factors and potential mechanisms. The results showed that: tDCS intervention has a significant effect on the endurance performance of the whole lower limbs, but there is no unified conclusion on the effect on the endurance performance of the knee joint. The researchers deem that tDCS can increase the excitability of the primary motor cortex and reduce the activation of the supplementary motor area and the premotor area to producing a lower rating of perceived exertion, but cannot affect the perception of exercise-induced pain, and stimulation protocols varied across studies, which may be partly responsible. This study can provide a theoretical basis for exploring the central mechanism of tDCS to improve endurance performance, formulating rehabilitation and sports training programsfor different groups of people, and developing new stimulation equipment to enhance the human body’s anti fatigue ability.

Effects of caffeine on central and peripheral fatigue following closed- and open-loop cycling exercises

We examined whether endurance performance and neuromuscular fatigue would be affected by caffeine ingestion during closed- and open-loop exercises. Nine cyclists performed a closed-loop (4,000-m cycling time trial) and an open-loop exercise (work rate fixed at mean power of the closed-loop trial) 60 min after ingesting caffeine (CAF, 5 mg/kg) or placebo (PLA, cellulose). Central and peripheral fatigue was quantified via pre- to post-exercise decrease in quadriceps voluntary activation and potentiated twitch force, respectively. Test sensitivity for detecting caffeine-induced improvements in exercise performance was calculated as the mean change in time divided by the error of measurement. Caffeine ingestion reduced the time of the closed-loop trial (PLA: 375.1±14.5 s vs CAF: 368.2±14.9 s, P=0.024) and increased exercise tolerance during the open-loop trial (PLA: 418.2±99.5 s vs CAF: 552.5±106.5 s, P=0.001), with similar calculated sensitivity indices (1.5, 90%CI: 0.7-2.9 vs 2.8, 90%CI: 1.9-5.1). The reduction in voluntary activation was more pronounced (P=0.019) in open- (-6.8±8.3%) than in closed-loop exercises (-1.9±4.4%), but there was no difference between open- and closed-loop exercises for the potentiated twitch force reduction (-25.6±12.8 vs -26.6±12.0%, P>0.05). Caffeine had no effect on central and peripheral fatigue development in either mode of exercise. In conclusion, caffeine improved endurance performance in both modes of exercise without influence on post-exercise central and peripheral fatigue, with the open-loop exercise imposing a greater challenge to central fatigue tolerance.

Footwear designed to enhance energy return improves running economy compared to a minimalist footwear: does it matter for running performance?

The present study compared the effects of a footwear designed to enhance energy return (thermoplastic polyurethane, TPU) vs minimalist shoes on running economy (RE) and endurance performance. In this counterbalanced and crossover design study, 11 recreational male runners performed two submaximal constant-speed running tests and two 3-km time-trials with the two shoe models. Oxygen uptake was measured during submaximal constant-speed running tests in order to determine the RE at 12 km/h and oxygen cost of running (CTO2) at individual average speed sustained during the 3-km running time-trials wearing either of the two shoes. Our results revealed that RE was improved (2.4%) with TPU shoes compared with minimalist shoes (P=0.01). However, there was no significant difference for CTO2 (P=0.61) and running performance (P=0.52) comparing the TPU (710±60 s) and the minimalist (718±63 s) shoe models. These novel findings demonstrate that shoes with enhanced mechanical energy return (i.e. TPU) produced a lower energy cost of running at low (i.e., 12 km/h) but not at high speeds (i.e., average speed sustained during the 3-km running time-trial, ∼15 km/h), ultimately resulting in similar running performance compared to the minimalist shoe.

Effects of Different Beverages Consumption on 21 km Running Performance and Physiological Functions in Female Recreational Marathon Runners / 中国运动医学杂志

Objective To compare the effect of a carbohydrate-electrolyte-protein solution (CEPS,2％ protein plus 4％ carbohydrate),carbohydrate-electrolyte solution (CES,6％ carbohydrate),and non-caloric sweetened placebo (PLA)on 21 km running performance of female recreational marathon runners.Methods In a randomized cross-over design,12 female recreational marathon runners (age:33.4 ± 2.1 years,body mass index:21.10 ± 0.6 kg/m2,and maximal oxygen consumption:48.5 ± 1.9 mL/kg/min)performed a 21 km time trial (TT)run on three occasions separated by at least 28 days.During the first 5 km,participants ran on the treadmill with 70％VO2max.Thereafter,the participants ran at whatever speed they wished for the remaining 16 km of the performance run.In each main trial,participants ingested the CEPS,CES,or PLA at a rate of 150 mL every 2.5 km.The blood samples,gas samples,heart rate,core temperature,and subjective measures were conducted every 5 km throughout the exercise.Results Time of TT run completion was slightly shorter (P ＜ 0.05)in the CES trial (97.8 ±1.6 min)than in the PLA trial (102.4 ± 2.4 min),with no significant differences between the CEPS trial (100.7 ± 2.9 min)and the other two trials (P＞0.05).There were no differences in core temperature,blood lactate,heart rate,CHO oxidation rate,fat oxidation rate,CHO oxidation amount,and fat oxidation amount among the different trials (all P＞0.05).The average blood glucose was higher in CES trial than PLA trial (P＜0.05).The average respiratory exchange rate was higher in CEPS trim than PLA trial (P＜0.05).Conclusion Compared with ingesting the PLA,ingesting the 6％ CES improves the 21 km TT run performance in recreational female runners.However,no additional benefit of CEPS was observed on endurance performance.

Influence of four weeks of n-3 polyunsaturated fatty acid supplementation on fat metabolism during prolonged exercise / 体力科学

Glycogen is an important source of energy production during endurance exercise, such as marathon. Due to limited storage of glycogen in muscle and liver, augmentation of fat oxidation is known to delay depletion of muscle glycogen, leading to improvement of endurance performance. N-3 polyunsaturated fatty acids (n-3 PUFA) resulting from the form of fish has shown to enhance fat oxidation at rest. However, effect of n-3 PUFA on substrate metabolism during prolonged exercise remains unclear. The present study was designed to investigate whether dietary n-3 PUFA enhances fat oxidation during exercise and endurance performance. Thirteen healthy men were divided into n-3 PUFA group [n=6, 6g/day of fish oil; 1,800mg eicosapentaenoic acid (EPA), 2,700mg docosahexiaenoic acid (DHA)] or CON group [n=7, 6g/day of olive oil]. The subjects ingested each supplement for 4-weeks. Before and after the treatment period, a 60-min pedaling exercise at 65% of maximal oxygen uptake followed by 5 km-time-trial was conducted. Resting concentrations of serum EPA and DHA, EPA/AA were significantly elevated in the n-3 PUFA group only. After supplementation period, the n-3 PUFA group increased significantly exercise-induced elevations of serum free fatty acids and glycerol concentrations, and lowered respiratory exchange ratio during a 60-min pedaling exercise. Similar changes were not observed in the CON group. However, treatment with n-3 PUFA did not affect significantly result of 5km-time-trial. Four-week supplementation of n-3 PUFA increased exercise-induced lipolysis and fat oxidation during prolonged exercise. However, the augmented fat metabolism did not affect endurance performance.

Energy system contribution in a maximal incremental test: correlations with pacing and overall performance in a 10-km running trial

This study aimed to verify the association between the contribution of energy systems during an incremental exercise test (IET), pacing, and performance during a 10-km running time trial. Thirteen male recreational runners completed an incremental exercise test on a treadmill to determine the respiratory compensation point (RCP), maximal oxygen uptake (V˙O2max), peak treadmill speed (PTS), and energy systems contribution; and a 10-km running time trial (T10-km) to determine endurance performance. The fractions of the aerobic (WAER) and glycolytic (WGLYCOL) contributions were calculated for each stage based on the oxygen uptake and the oxygen energy equivalents derived by blood lactate accumulation, respectively. Total metabolic demand (WTOTAL) was the sum of these two energy systems. Endurance performance during the T10-km was moderately correlated with RCP, V˙O2maxand PTS (P<@0.05), and moderate-to-highly correlated with WAER, WGLYCOL, and WTOTAL (P<0.05). In addition, WAER, WGLYCOL, and WTOTAL were also significantly correlated with running speed in the middle (P<0.01) and final (P<0.01) sections of the T10-km. These findings suggest that the assessment of energy contribution during IET is potentially useful as an alternative variable in the evaluation of endurance runners, especially because of its relationship with specific parts of a long-distance race.

Relationship between CO2 excess due to lactic acid production during exercise and endurance performance / 体力科学

A study was conducted to assess the relationship between CO<SUB>2</SUB> excess due to lactic acid production during exercise and endurance performance in order to clarify the availability of CO<SUB>2</SUB> excess as an index of endurance capacity. Four healthy males (control group; CON) aged 21-24 years, and six male long-distance runners (LDR) aged 18-22 years, were subjected to incremental maximal testing on a cycle ergometer and 12-min exhaustive track running. The results obtained are summarized as follows.<BR>1) Mean values (±SD) of CO<SUB>2</SUB> excess (m<I>l</I>) were 3, 442±677 m<I>l</I> for LDR and 2, 667±437 m<I>l</I> for CON, respectively. On the other hand, the mean value of CO<SUB>2</SUB> excess per unit body weight (CO<SUB>2</SUB> excess/w) obtained in LDR (59.1±9.07 m<I>l</I>⋅kg<SUP>-1</SUP>) was significantly higher than that in CON (40.3±3.54 m<I>l</I>⋅kg<SUP>-1</SUP>) (p<0.01) .<BR>2) The ratio of CO<SUP>2</SUP> excess/w to ΔLA (the difference between blood lactate at 1 min after exercise and that at rest) showed a tendency to be higher in LDR (5.59±1.16 m<I>l</I>⋅kg<SUP>-1</SUP>⋅mmol<SUP>-1</SUP>) than in CON (4.46±0.69 m<I>l</I>⋅kg<SUP>-1</SUP>⋅mmol<SUP>-1</SUP>) . However, there was no significant difference between these two groups in the ratio of CO<SUP>2</SUP> excess/w to ΔLA.<BR>3) The CO<SUP>2</SUP> excess/w (m<I>l</I>⋅kg<SUP>-1</SUP>) was significantly related to Vo<SUB>2</SUB>max (r=0.813, p<0.01) and Vo<SUB>2</SUB>AT (r=0.892, p<0.001), respectively. Moreover, CO<SUB>2</SUB> excess/w was significantly correlated with ΔHCO<SUB>3</SUB>- (the difference between blood bicarbonate at l min after exercise and that at rest) (r=0.649, p<0.05) .<BR>4) The CO<SUB>2</SUB> excess (m<I>l</I>) and CO<SUB>2</SUB> excess/w (m<I>l</I>⋅kg<SUP>-1</SUP>) were significantly correlated with 12-min exhaustive running performance (r=0.715, p<0.05, r=0.933, p<0.001), as was the ratio of CO<SUB>2</SUB> excess/w to d LA (r=0.671, p<0.05) .<BR>5) From these results, it was suggested that the CO<SUB>2</SUB> excess/w and the ratio of CO<SUB>2</SUB> excess/w to ΔLA could be important factors related to performance of endurance exercise (i. e., 3, 000-5, 000 m running) accompanied by blood lactate accumulation.

The effects of carbohydrate loading on the muscle glycogen content and the bicycling performance in healthy Japanese men / 体力科学

This study was undertaken to examine whether carbohydrate loading gives a good effect to improve the endurance performance in Japanese subjects who had habitually eaten carbohydrate-rich diets. The glycogen content of the vastus lateralis muscle was determined in 6 healthy male subjects with the aid of the needle biopsy technique by setting different diets after glycogen store was depleted by exhaustive exercise.<BR>Glycogen content of the vastus lateralis muscle after mix, low and high carbohydrate diets was 22.7±2.0, 11.6±1.6 and 36.6±4.5 g/wet muscle⋅kg (mean±SD), respectively, while exhaustive time was 75′39″±10′02″, 67′58″±14′11″and 92′10″±22′10″ (mean±SD), respectively. Thus, a good correlation was noted between muscle glycogen content and work time.<BR>It was therefore concluded that the glycogen content of the working muscle was a determinant factor for the capacity to perform long-term heavy exercise and that carbohy-drate loading attained with low carbohydrate diet and exhaustive exercise followed by high carbohydrate diet had a good effect to perform heavy exercise even in Japanese who lived on carbohydrate-rich diet.

SIGNIFICANCE OF ANAEROBIC THRESHOLD IN THE PREDICTION AND DETERMINATION OF ENDURANCE PERFORMANCE IN ATHLETES / 中国运动医学杂志

The purpose of this study was to explore the significance of AT nn the prediction and determination of endurance performance in 60 athletes, including long distance runners, marathoners and cyclists. 17 nonendurance athletes served as control group. Every subject performed an. incremental exercise test on Monark cycle ergometer. The work rate was increased in steps of 30W/min until the subject was unable to sustain the workrate. The Vo_2, Vco_2 and Mets werecontinually measured during and after test by MMC of Beckman company The test and retest of AT were made in 14 long distance runners in their one-year training cycle. On the basis of the results the prediction of the endurance performance was done before competition After competition the determination of endurance performance and positive rate for variables and correlation. coefficient to AT were summarized. All calculated performance: variables correlated the 1500m, and 10,000m with r=0.68 and r=0.80 respectively. In conclusion, the results of the study confirmed the high significance of AT in the prediction of endurance performance in athletes.