Influence of carbohydrate on serum caffeine concentrations following caffeine ingestion

ObjectivesTo examine the effect of a high carbohydrate meal on serum caffeine concentration following caffeine intake.DesignRandomised, double-blind, crossover.MethodsFourteen healthy males randomly completed 4 trials, each separated by 5 days. Participants either remained fasted (on 2 occasions) or ingested a high carbohydrate meal (2.0 g kg^?1 carbohydrate, 42.4 ± 0.6 kJ kg^?1) prior to consuming either 6 or 9 mg kg^?1 anhydrous caffeine. Venous blood was sampled for the analysis of serum caffeine at baseline and at 6 time-points over 4 h following caffeine intake.ResultsPeak caffeine concentration occurred 60 min following ingestion for both the 6 and 9 mg kg^?1 fasted (p < 0.001) trials compared to 120 and 180 min following ingestion for the 6 and 9 mg kg^?1 fed trials, respectively (p < 0.001). Peak concentration was greater in the 9 mg kg^?1 fasted trial than the corresponding fed condition (70 ± 9 μmol L^?1 and 56 ± 6 μmol L^?1, respectively) and both were greater than the 6 mg kg^?1 conditions (44 ± 8 μmol L^?1 and 38 ± 8 μmol L^?1 for 6 mg kg^?1 fasted and fed, respectively). Area under the caffeine curve was significantly greater (p < 0.001) in the 9 mg kg^?1 fasted trial (3262 μmol L^?1 h^?1), whilst areas were lowest in the 6 mg kg^?1 fed trial (1644 μmol L^?1 h^?1).ConclusionsA high carbohydrate meal consumed prior to caffeine ingestion significantly reduced serum caffeine concentrations and delayed time to peak concentration. Differences in research findings between caffeine supplementation studies may, at least in part, be related to variations in postprandial timing of caffeine intake. The influence of postprandial timing should be considered when athletes consume caffeine with the aim of enhancing performance.     

Effect of stage duration on maximal heart rate and post-exercise blood lactate concentration during incremental treadmill tests

ObjectivesThis study compared the responses during maximal incremental treadmill tests of 1-min, 2-min, and 3-min stage durations mainly in terms of maximal heart rate (HR_max) and peak blood lactate concentration (LA_peak).DesignRepeated-measures.MethodsThirty-four male, recreational, endurance-trained runners (40 ± 13 years) performed three tests on a motorized treadmill. The tests started at 8 km h^?1 with increments of 1 km h^?1 every 1 min for the short-stage protocol, every 2 min for the intermediate-stage protocol, and every 3 min for the long-stage protocol. LA_peak was defined for each subject as the highest value among the lactate concentrations determined at the end of each test and at the third, fifth and seventh minutes after test, during passive recovery.ResultsAnalysis of variance revealed a significant effect of the stage duration on the HR_max (p = 0.003) and LA_peak (p = 0.001). The HR_max was higher in the intermediate-stage compared to the short-stage protocol (184.8 ± 12.7 vs. 181.8 ± 12.1 beats min^?1, p < 0.001), but no significant differences were found between the long-stage (183.1 ± 12.1 beats min^?1) and the intermediate-stage or short-stage protocols (p > 0.05). The LA_peak was lower in the long-stage compared to the short-stage and intermediate-stage protocols (7.9 ± 2.2 vs. 9.4 ± 2.2 and 9.2 ± 1.9 mmol L^?1, respectively, p < 0.05). Further, blood lactate reached peak concentration at the fifth minute after test for all the protocols.ConclusionsThus, HR_max and LA_peak depend on the stage duration of the incremental test, but the moment at which blood lactate reaches peak concentration is independent of the duration. Further, we suggest 2-min stage duration protocols to determine HR_max.     

Coinciding exercise with peak serum caffeine does not improve cycling performance

ObjectivesTo investigate whether coinciding peak serum caffeine concentration with the onset of exercise enhances subsequent endurance performance.DesignRandomised, double-blind, crossover.MethodsIn this randomised, placebo-controlled, double-blind crossover study, 14 male trained cyclists and triathletes (age 31 ± 5 year, body mass 75.4 ± 5.7 kg, VO₂max 69.5 ± 6.1 mL kg^?1 min^?1 and peak power output 417 ± 35 W, mean ± SD) consumed 6 mg kg^?1 caffeine or a placebo either 1 h (C_1 h) prior to completing a 40 km time trial or when the start of exercise coincided with individual peak serum caffeine concentrations (C_peak). C_peak was determined from a separate ‘caffeine profiling’ session that involved monitoring caffeine concentrations in the blood every 30 min over a 4 h period.ResultsFollowing caffeine ingestion, peak serum caffeine occurred 120 min in 12 participants and 150 min in 2 participants. Time to complete the 40 km time trial was significantly faster (2.0%; p = 0.002) in C_1 h compared to placebo. No statistically significant improvement in performance was noted in the C_peak trial versus placebo (1.1%; p = 0.240). Whilst no differences in metabolic markers were found between C_peak and placebo conditions, plasma concentrations of glucose (p = 0.005), norepinephrine and epinephrine (p ≤ 0.002) were higher in the C_1 h trial 6 min post-exercise versus placebo.ConclusionsIn contrast to coinciding peak serum caffeine concentration with exercise onset, caffeine consumed 60 min prior to exercise resulted in significant improvements in 40 km time trial performance. The ergogenic effect of caffeine was not found to be related to peak caffeine concentration in the blood at the onset of endurance exercise.     

Diminutions of acceleration and deceleration output during professional football match play

ObjectivesThis study examined distances covered at low (1–2 m s^?2), moderate (2–3 m s^?2) and high (>3 m s^?2) acceleration (L_ACC, M_ACC and H_ACC respectively) and deceleration (L_DEC, M_DEC, and H_DEC respectively) during competitive football games. Temporal and transient patterns of acceleration and deceleration were also examined.DesignObservational, repeated measures.MethodsThirty-six professional male professional footballers were monitored using a 10 Hz non-differential global positioning system (NdGPS). Match data was organised into six 15 min periods (P1: 1–15 min, P2: 16–30 min, P3: 31–45 min, P4: 46–60 min, P5: 61–75 min, and P6: 76–90 min) for analysis of temporal patterns, and into eighteen 5 min periods for analysis of transient patterns. ANOVA with Bonferroni post hoc tests were used to identify significant (p < 0.05) differences between periods.ResultsDistance covered at L_ACC, M_ACC, H_ACC, L_DEC, M_DEC, and H_DEC was 424 ± 75 m, 242 ± 25 m, 178 ± 38 m, 365 ± 54 m, 210 ± 23 m and 162 ± 29 m respectively. Between period decrements ranged from 8.0% to 13.2% from P1 to P3, 9.2% to 16.3% from P4 to P6, and from 14.9% to 21.0% from P1 to P6. Following PEAK H_ACC (148% of mean 5 min H_ACC), H_ACC at 5_POST was 10.4% lower than mean (p < 0.01).ConclusionsTime-dependent reductions in distances covered suggest that acceleration and deceleration capability are acutely compromised during match play. Further, the occurrence of transient fatigue may be supported by the findings that H_ACC and H_DEC performance following PEAK was approximately 10% lower than mean values.     

Dietary supplementation with New Zealand blackcurrant extract enhances fat oxidation during submaximal exercise in the heat

ObjectivesThis study investigated the effect of 7 days’ supplementation with New Zealand blackcurrant extract on thermoregulation and substrate metabolism during running in the heat.DesignRandomized, double-blind, cross-over study.MethodsTwelve men and six women (mean ± SD: Age 27 ± 6 years, height 1.76 ± 0.10 m, mass 74 ± 12 kg, V̇O_2max 53.4 ± 7.0 mL kg⁻¹ min⁻¹) completed one assessment of maximal aerobic capacity and one familiarisation trial (18 °C, 40% relative humidity, RH), before ingesting 2 × 300 mg day⁻¹ capsules of CurraNZ™ (each containing 105 mg anthocyanin) or a visually matched placebo (2 × 300 mg microcrystalline cellulose M102) for 7 days (washout 14 days). On day 7 of each supplementation period, participants completed 60 min of fasted running at 65% V̇O_2max in hot ambient conditions (34 °C and 40% relative humidity).ResultsCarbohydrate oxidation was decreased in the NZBC trial [by 0.24 g min⁻¹ (95% CI: 0.21–0.27 g min^-1)] compared to placebo (p =  0.014, d = 0.46), and fat oxidation was increased in the NZBC trial [by 0.12 g min⁻¹ (95% CI: 0.10 to 0.15 g min⁻¹)], compared to placebo (p = 0.008, d = 0.57). NZBC did not influence heart rate (p = 0.963), rectal temperature (p = 0.380), skin temperature (p = 0.955), body temperature (p = 0.214) or physiological strain index (p = 0.705) during exercise.ConclusionsSeven-days intake of 600 mg NZBC extract increased fat oxidation without influencing cardiorespiratory or thermoregulatory variables during prolonged moderate intensity running in hot conditions.     

Dose-response between frequency of breaks in sedentary time and glucose control in type 2 diabetes: A proof of concept study

ObjectivesThis study aimed to investigate dose-response between frequency of breaks in sedentary time and glucose control.DesignRandomised three-treatment, two-period balanced incomplete block trial.MethodsTwelve adults with type 2 diabetes (age, 60 ± 11 years; body mass index, 30.2 ± 4.7 kg/m²) participated in two of the following treatment conditions: sitting for 7 h interrupted by 3 min light-intensity walking breaks every (1) 60 min (Condition 1), (2) 30 min (Condition 2), and (3) 15 min (Condition 3). Postprandial glucose incremental area under the curves (iAUCs) and 21-h glucose total area under the curve (AUC) were measured using continuous glucose monitoring. Standardised meals were provided.ResultsCompared with Condition 1 (6.7 ± 0.8 mmol L⁻¹ × 3.5 h⁻¹), post-breakfast glucose iAUC was reduced for Condition 3 (3.5 ± 0.9 mmol L⁻¹ × 3.5 h⁻¹, p ˂ 0.04). Post-lunch glucose iAUC was lower in Condition 3 (1.3 ± 0.9 mmol L⁻¹ × 3.5 h⁻¹, p ˂ 0.03) and Condition 2 (2.1 ± 0.7 mmol L⁻¹ × 3.5 h⁻¹, p ˂ 0.05) relative to Condition 1 (4.6 ± 0.8 mmol L⁻¹ × 3.5 h⁻¹). Condition 3 (1.0 ± 0.7 mmol L⁻¹ × 3.5 h⁻¹, p = 0.02) and Condition 2 (1.6 ± 0.6 mmol L⁻¹ × 3.5 h⁻¹, p ˂ 0.04) attenuated post-dinner glucose iAUC compared with Condition 1 (4.0 ± 0.7 mmol L⁻¹ × 3.5 h⁻¹). Cumulative 10.5-h postprandial glucose iAUC was lower in Condition 3 than Condition 1 (p = 0.02). Condition 3 reduced 21-h glucose AUC compared with Condition 1 (p < 0.001) and Condition 2 (p = 0.002). However, post-breakfast glucose iAUC, cumulative 10.5-h postprandial glucose iAUC and 21-h glucose AUC were not different between Condition 2 and Condition 1 (p ˃ 0.05).ConclusionsThere could be dose-response between frequency of breaks in sedentary time and glucose. Interrupting sedentary time every 15 min could produce better glucose control.     

Malignant breast tumours: Correlation of apparent diffusion coefficient values using diffusion-weighted images and dynamic contrast-enhancement ratio with histologic grading

PurposeTo evaluate the correlation of the apparent diffusion coefficient (ADC) using diffusion weighted imaging (DWI) and early/delayed enhancement (E/D) ratio using dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) with histological grading in malignant breast lesions.Material and methodsThirty-one women with 34 histopathologically proved malignant breast lesions underwent MRI within 2 weeks prior to surgery. MRI examination included T1 and T2 W sequences, DWI and DCE-MRI. ADC values and E/D ratios are correlated with the histological grades.ResultsThe mean ADC of the malignant lesions was 0.85 ± 0.12 × 10^?3 mm²/s. The mean ADC values of grade I, II and III were 0.96 ± 0.12 × 10^?3 mm²/s, 0.87 ± 0.07 × 10^?3 mm²/s and 0.75 ± 0.12 × 10^?3 mm²/s, respectively. Tumours with higher grade showed significantly lower ADC value (p = 0.0001) compared with lower grade and there is an inverse correlation between ADC value and histological grade (r = ?0.62, p-value = 0.0001). The mean E/D ratio for grade I, II and III tumours were 0.98 ± 0.04, 1.01 ± 0.05 and 1.07 ± 0.08, respectively. Tumours with higher grade showed significantly higher E/D ratio (p = 0.005) compared with lower grade and there was a direct correlation between E/D ratio and histological grade (r = 0.44, p = 0.008).ConclusionDWI is a useful diagnostic parameter with significantly higher correlation with the histological grade of breast cancer than DCE MRI, which is an important factor for proper treatment selection.     

Effect of induced alkalosis on performance during a field-simulated BMX cycling competition

Objectives

The aim of the present study was to test the effect of sodium bicarbonate (NaHCO₃^?) ingestion on performance during a simulated competition on a Bicycle Motocross (BMX) track.

Relationship between rowing ergometer performance and physiological responses to upper and lower body exercises in rowers

The aim of this investigation was to compare the physiological responses of 2000 m rowing ergometer test with 7-min bench pull and leg press tests. We hypothesised that leg press exercise contributes to 2000 m rowing ergometer test results, rather than bench pull performed by arms. College level rowers (n = 12) performed 2000 m rowing test and after one day 7-min bench pull and leg press (50% from the 1 RM). Stroke rate, heart rate (HR), blood lactate (LA) and ratings of perceived exertion (RPE) were measured during all tests. The number of repetitions was highest during 2000 m rowing test (194.2 ± 19.5) and lowest during bench pull (122.6 ± 17.7) (during leg press 173.5 ± 11.8). Differences between 2000 m rowing test, leg press and bench pull tests were significant in mean and maximal HR. In LA concentration, the highest values were at 3rd min of recovery after rowing test (14.8 ± 1.7 mmol l^?1). Between bench pull (8.8 ± 1.9 and 8.5 ± 2.7 mmol l^?1) and leg press (11.8 ± 2.5 and 11.2 ± 2.3 mmol l^?1) tests, the difference in LA concentration was not significant (p > 0.05). Ratings of perceived exertion were highest in 2000 m rowing test (19.3 ± 0.9), difference with leg press and bench pull tests was not significant. There were significant relationships in mean and maximal HR (r = 0.713–0.767) and Borg scale (r = 0.764) during rowing test and leg press. The number of repetitions during leg press exercise correlated significantly with rowing test time (r = ?0.677). In conclusion, this study suggests that in rowers there are major differences in the physiological adaptation to upper body and leg exercise, performed at similar intensities. Leg press exercise could be used to measure sport-specific strength endurance in rowers.     

Accelerometer detected lateral sway during a submaximal running test correlates with endurance exercise performance in elite Australian male cricket players

ObjectiveTo identify whether movement patterns during a standardized submaximal running test (SSRT), assessed by accelerometry, were associated with improvements in endurance exercise performance.DesignA retrospective analysis of data collected from the 2018–2019 Australian cricket preseason.MethodsThirty-nine high-performance male cricket players were studied (25 ± 3 years, 82 ± 6 kg, 183 ± 6 cm). SSRT was performed monthly prior to a two kilometre (km) running time trial (2 kmTT). SSRT involved running between markers, positioned twenty metres apart, for three minutes. Foot strikes were timed to a metronome (154 beats/min) to elicit a running speed of ˜eight km/h. Triaxial accelerometers were worn in vests on the upper back and used to assess PlayerLoad medio-lateral vector (PL1D_side%), vertical vector (PL1D_up%) and anterior-posterior vector (PL1D_fwd%) were assessed.Results2 kmTT performance improved over the study period (p < 0.05). PlayerLoad vectors during the first minute of SSRT were not related to 2 kmTT performance (p > 0.23). During the second and third minutes there were positive associations between 2 kmTT (run time) and PL1D_side% (SSRT_2min, β 2.12, p < 0.03, 95% CI: 0.22–4.01; SSRT3_min, β 2.30, p < 0.03, 95% CI:0.32–4.29), but not PL1D_up% (SSRT_2min, β −0.15, p = 0.77, 95% CI: −1.13–0.83; SSRT_3min, β −0.15, p = 0.77, 95% CI: −1.11–0.87) or PL1D_fwd% (SSRT_2min, β −0.45, p = 0.42, 95% CI: −1.49–0.62; SSRT_3min, B−0.45, p = 0.40, 95% CI: −1.51–0.60).ConclusionAssessment of PL1D_side% during the second or third minutes of SSRT may inform how an athlete’s endurance exercise performance is responding to changes in training load.     

Evaluation of inactive adults’ ability to maintain a moderate-intensity walking pace

ObjectivesTo determine self-selected brisk walking pace in currently inactive adults and investigate the efficacy of rhythmic auditory stimuli to regulate moderate intensity walking.DesignA single-sample controlled laboratory design.MethodsCurrently inactive adults (N = 25; 76% female; age = 34 ± 13 yr) completed a moderate intensity treadmill walking trial, during which cadence and steady-state O₂ were measured. Participants then completed a 10-min self-paced “brisk” walk followed by a 10-min moderate-paced walk, prompted by a clip-on metronome matched to the treadmill cadence. Data were analyzed using RM t-test, Cohen's d, Bland–Altman plot, and one-way RM ANOVA.ResultsMean energy expenditure and cadence during the treadmill trial were 3.88 ± 0.53 METs and 114 ± 8 steps min^?1. During self-paced brisk walking cadence was 124 ± 8 steps min^?1. Cadence during metronome-paced walking was slower for all participants (114 ± 8 steps min^?1; p < 0.05, d = 1.23). From the Bland–Altman plots, 23 participants walked within ±3 steps min^?1 of the metronome cadence, and the other 2 participants were within ±10 steps min^?1. There were no significant differences (p > 0.05) among the minute-by-minute cadences across the 10 min of either condition.ConclusionsEnergy expenditure during 2.7 mph treadmill walking was higher than 3 METs. Inactive adults walk at a higher cadence during “brisk” walking, compared to walking at a metronome-guided moderate pace. While the natural walking pace of inactive adults was at an intensity known to produce health benefits, and was maintained for 10 min, the use of rhythmic auditory feedback is an effective method for regulating walking at a prescribed intensity in inactive adults.     

Match demands of professional Futsal: A case study

Despite its popularity and competitive status there have been only few scientific studies that have examined Futsal in professional players. Consequently the aim of this study was to examine the physiological responses and activity pattern to Futsal simulated game-play in professional players. Eight full-time professional outfield Futsal players volunteered for this study: age 22.4 (95% CI 18.8–25.3) years, body mass 75.4 (60–91) kg, height 1.77 (1.59–1.95) m and VO_2max 64.8 (53.8–75.8) ml kg^?1 min^?1. Physiological measurements were assessed during highly competitive training games (4 × 10-min quarters) and consisted of game VO₂, game blood-lactate concentration ([la]_b) and game heart rates (HRs). Game activities were assessed using a computerised video-analysis system. During simulated game-play players attained 75% (59–92) and 90% (84–96) of VO_2max and HR_max, respectively. Mean game VO₂ was 48.6 (40.1–57.1) ml kg^?1 min^?1. Peak game VO₂ and HRs were 99% (88–109) and 98% [90–106] of laboratory maximal values, respectively. Players spent 46 and 52% of the playing time at exercise intensities higher than 80 and 90% of VO_2max and HR_max, respectively. Mean [la]_b was 5.3 (1.1–10.4) mmol l^?1. Players covered 121 (105–137) m min^?1 and 5% (1–11) and 12% (3.8–19.5) of playing time spent performing sprinting and high-intensity running, respectively. On average players performed a sprint every ～79 s during play. These results show that Futsal played at professional level is a high-intensity exercise heavily taxing the aerobic and anaerobic pathways.     

The effects of multidirectional soccer-specific fatigue on markers of hamstring injury risk

The purpose of this work was to investigate the effect of multidirectional soccer-specific fatigue on hamstring muscle strength and angle of peak torque. Sixteen male semi-professional soccer players (mean ± S.D.: age: 21.3 ± 2.9 years; height 185.0 ± 8.7 cm; body mass 81.6 ± 6.7 kg) completed the SAFT⁹⁰, a multidirectional, intermittent 90-min exercise protocol based on data from English Championship soccer matches. Prior to exercise (t₀), at half-time (t₄₅) and post-exercise (t₁₀₅), subjects performed three maximal dominant limb isokinetic contractions (Biodex, System 3) at 120° s^?1 through a 90° range for concentric and eccentric knee flexors and concentric knee extensors. Analysis of variance revealed significant time dependant reductions in gravity corrected eccentric hamstring peak torque, and consequently in the functional hamstring:quadriceps ratio (P < 0.01). Eccentric hamstring peak torque decreased significantly during each half (t₀: 272.0 ± 43.2; t₄₅: 240.4 ± 43.3; t₁₀₅: 226.3 ± 45.7 N m). The functional hamstring:quadriceps ratio also decreased significantly during each half (t₀: 116.6 ± 21.2; t₄₅: 107.1 ± 17.6; t₁₀₅: 98.8 ± 20.3%). There were no significant changes in concentric hamstring or quadriceps peak torque observed during SAFT⁹⁰ (P > 0.05). Data analysis also revealed significant differences for Angle of Peak Torque for eccentric hamstrings (P < 0.05) which was significantly higher at the end of each half (t₄₅: 37 ± 15; t₁₀₅: 38 ± 18°) than the pre-exercise value (t₀: 28 ± 12°). There was a time dependant decrease in peak eccentric hamstring torque and in the functional strength ratio which may have implications for the increased predisposition to hamstring strain injury during the latter stages of match-play.     

DHA-rich fish oil lowers heart rate during submaximal exercise in elite Australian Rules footballers

Omega-3 fatty acids (n-3) can improve cardiovascular (CV) function. This study examined the effects of n-3 on endurance performance, recovery and CV risk factors in elite Australian Rules football players. 25 players were randomised, double-blind, to 6 g/day of docosahexaenoic acid (DHA)-rich fish oil (FO; n = 12) or sunflower oil (SO; n = 13) during 5 weeks of training. At baseline erythrocyte n-3 content, resting blood pressure (BP), fasting serum triglycerides (TG) and heart rate (HR) during treadmill running at 10 km/h were assessed. Two treadmill runs (T1 and T2) to exhaustion, separated by 5 min, were then performed at the average speed for a recent 2200 m time-trial. After 5 weeks, erythrocyte n-3 increased (FO 3.8 ± 0.6%, SO 0.6 ± 0.3%; P < 0.001) while TG (FO ?0.32 ± 0.09 mmol l^?1, SO 0.08 ± 0.05 mmol l^?1; P < 0.001), diastolic BP (FO 1.3 ± 1.3 mmHg, SO 6.8 ± 1.7 mmHg; P = 0.04) and HR during submaximal exercise (FO ?7.8 ± 2.3 beats min^?1, SO ?1.9 ± 1.9 beats min^?1; P = 0.03) decreased in FO compared with SO. Time to exhaustion (TTE) during T1 increased by Week 5 (FO 10.2 ± 2.2%, SO 17.3 ± 4.3%; P < 0.001 for time). Recovery (TTE for T2 as % T1) decreased in both groups (FO, ?3.4 ± 4.5%, SO ?8.8 ± 3.9%; P = 0.05 for time). We conclude that 5 weeks of supplementation with FO improved CV function and reduced CV risk factors, but did not improve endurance performance or recovery in elite Australian Rules footballers.     

Heart rate and blood lactate responses during Taekwondo training and competition

ObjectiveThe study investigated physical fitness characteristics of elite Taekwondo (TKD) players as well as their heart rate (HR) response and blood lactate concentration changes during TKD specific exercises and simulated competition.MethodsAnaerobic and aerobic power has been evaluated in eight elite TKD players (age: 20 ± 1 years, body mass: 70.8 ± 6 kg, Ht: 179.9 ± 4 cm). We also measured heart rate and blood lactate concentration during competition and specific-exercises (front kicks during 10 s, 1 and 3 min).ResultsMaximum oxygen uptake (VO₂max) and peak anaerobic power (Wpeak) averaged 56.22 ± 2.57 ml min^–1 kg^–1 and 12.1 ± 1.7 W kg^–1, respectively. HR and blood lactate [La] concentrations increased significantly during competition (F = 19.4, P < 0.001; F = 21.3, P < 0.001) compared to the resting value. HR and [La] values were significantly correlated with those measured during 10 s (R = 0.85, P < 0.05 and R = 0.79, P < 0.05, respectively) and 3-min specific exercises (R = 0.95, P < 0.01 and R = 0.76, P < 0.05).ConclusionsTKD requires high levels of both aerobic and anaerobic physical fitness. The correlation between specific exercises and competition is of practical interest for TKD players and trainers.     

Physiological factors determining downhill vs uphill running endurance performance

ObjectivesRecent studies investigated the determinants of trail running performance (i.e., combining uphill (UR) and downhill running sections (DR)), while the possible specific physiological factors specifically determining UR vs DR performances (i.e., isolating UR and DR) remain presently unknown. This study aims to determine the cardiorespiratory responses to outdoor DR vs UR time-trial and explore the determinants of DR and UR performance in highly trained runners.DesignRandomized controlled trial.MethodsTen male highly-trained endurance athletes completed 5-km DR and UR time-trials (average grade: ±8%) and were tested for maximal oxygen uptake, lower limb extensor maximal strength, local muscle endurance, leg musculotendinous stiffness, vertical jump ability, explosivity/agility and sprint velocity. Predictors of DR and UR performance were investigated using correlation and commonality regression analyses.ResultsRunning velocity was higher in DR vs UR time-trial (20.4 ± 1.0 vs 12.0 ± 0.5 km·h^?1, p < 0.05) with similar average heart rate (95 ± 2% vs 94 ± 2% maximal heart rate; p > 0.05) despite lower average V?O₂ (85 ± 8% vs 89 ± 7% V?O_2max; p < 0.05). Velocity at V?O_2max (vV?O_2max) body mass index (BMI) and maximal extensor strength were significant predictors of UR performance (r² = 0.94) whereas vV?O_2max, leg musculotendinous stiffness and maximal extensor strength were significant predictors of DR performance (r² = 0.84).ConclusionsFive-km UR and DR running performances are both well explained by three independent predictors. If two predictors are shared between UR and DR performances (vV?O_2max and maximal strength), their relative contribution is different and, importantly, the third predictor appears very specific to the exercise modality (BMI for UR vs leg musculotendinous stiffness for DR).     

Whole-body biomechanical load in running-based sports: The validity of estimating ground reaction forces from segmental accelerations

ObjectivesUnlike physiological loads, the biomechanical loads of training in running-based sports are still largely unexplored. This study, therefore, aimed to assess the validity of estimating ground reaction forces (GRF), as a measure of external whole-body biomechanical loading, from segmental accelerations.MethodsFifteen team-sport athletes performed accelerations, decelerations, 90° cuts and straight running at different speeds including sprinting. Full-body kinematics and GRF were recorded with a three-dimensional motion capture system and a single force platform respectively. GRF profiles were estimated as the sum of the product of all fifteen segmental masses and accelerations, or a reduced number of segments.ResultsErrors for GRF profiles estimated from fifteen segmental accelerations were low (1–2 N kg⁻¹) for low-speed running, moderate (2–3 N kg⁻¹) for accelerations, 90° cuts and moderate-speed running, but very high (>4 N kg⁻¹) for decelerations and high-speed running. Similarly, impulse (2.3–11.1%), impact peak (9.2–28.5%) and loading rate (20.1–42.8%) errors varied across tasks. Moreover, mean errors increased from 3.26 ± 1.72 N kg⁻¹ to 6.76 ± 3.62 N kg⁻¹ across tasks when the number of segments was reduced.ConclusionsAccuracy of estimated GRF profiles and loading characteristics was dependent on task, and errors substantially increased when the number of segments was reduced. Using a direct mechanical approach to estimate GRF from segmental accelerations is thus unlikely to be a valid method to assess whole-body biomechanical loading across different dynamic and high-intensity activities. Researchers and practitioners should, therefore, be very cautious when interpreting accelerations from one or several segments, as these are unlikely to accurately represent external whole-body biomechanical loads.     

Laboratory experiments to characterize radiochloride diffusion in unsaturated soils

Diffusion transport of ³⁶Cl was examined in seven soils under unsaturated conditions in tubes packed with two portions of each soil having different ³⁶Cl activity concentrations. Apparent diffusion coefficients (D_a) derived from diffusion profiles varied within a narrow range (from 3×10^?10 to 7×10^?10 m² s^?1) confirming the minor effect of soil properties on the diffusion of a non-reactive radionuclide like ³⁶Cl. Instead, packing conditions had a major effect. Solid–liquid distribution coefficients (K_d) derived from D_a (0.02–0.2 L kg^?1) were systematically lower than those obtained from batch experiments (0.6–1.0 L kg^?1), but with a similar variation pattern among soils. The low values of K_d (Cl) confirmed an almost negligible radiochloride–soil interaction.     

A comparison of acute glycaemic responses to accumulated or single bout walking exercise in apparently healthy,insufficiently active adults

ObjectivesTo investigate the acute glyacaemic response to accumulated or single bout walking exercise in apparently healthy adults.DesignThree arm, randomised crossover control study.MethodsTen adults (age: 50 ± 12.6 y; BMI 29.0 ± 5.4 kg m⁻²) completed three separate trials comprising three 10-min walking bouts after breakfast, lunch, and dinner (APPW), a single 30-min walking bout after dinner only (CPPW), or a no-exercise control (NOEX). Participants walked on a treadmill at a moderate intensity of 55%–70% heart rate reserve. Two-hour postprandial glucose response was assessed using a continuous glucose monitor.ResultsThere was a difference in the pattern of the glucose response between the trials during the two hours following dinner (p < 0.001). Postprandial dinner glucose concentrations were not different between APPW and CPPW but were up to 1.01 mmol L⁻¹ lower than NOEX (partial eta² = 0.21, p = 0.041).ConclusionsTen minutes of moderate intensity walking completed 30 min after each meal lowers postprandial dinner glucose concentrations in comparison to no-exercise, and reduces glucose by a similar magnitude as a single 30-min bout after the evening meal. Short bouts of exercise after each meal may be recommended to minimise glucose elevations after dinner that might increase risk of cardiometabolic disease.