Heat stress impairs proprioception but not running mechanics

ObjectivesTo determine the effects of heat stress on ankle proprioception and running gait pattern.DesignCounterbalanced repeated measures.Methods12 trained runners performed a proprioception test (active movement discrimination) before and immediately after a 30 min, self-paced treadmill run in HOT (39 °C) and COOL (22 °C) ambient conditions. Velocity was imposed during the first and last minute (70% of maximal aerobic velocity, 13.3 ± 0.8 km h⁻¹) for determination of running mechanics and spring–mass characteristics.ResultsRectal (39.7 ± 0.4 vs. 39.4 ± 0.4 °C), skin (36.3 ± 1.1 vs. 31.8 ± 1.1 °C) and average body (38.3 ± 0.2 vs. 36.4 ± 0.4 °C) temperatures together with heart rate (178 ± 8 vs. 174 ± 6 bpm) and thermal discomfort (6.5 ± 0.5 vs. 4.3 ± 1.3) were all higher at the end of the HOT compared to COOL run (all p < 0.05). Distance covered was lower in HOT than COOL (−5.1 ± 3.6%, p < 0.001). Average error during the proprioception test increased after running in HOT (+11%, p < 0.05) but not in COOL (−2%). There was no significant difference for most segmental and joint angles at heel contact, except for a global increase in pelvis retroversion and decrease in ankle dorsi-flexion angles with time (p < 0.05). Step frequency decreased (−2.5 ± 3.6%) and step length increased (+2.6 ± 3.8%) over time (p < 0.05), independently of condition. Spring–mass characteristics remained unchanged (all p > 0.05).ConclusionsHeat stress exacerbates thermal, cardiovascular and perceptual responses, while running velocity was slower during a 30 min self-paced treadmill run. Heat stress also impairs ankle proprioception during an active movement discrimination task, but it has no influence on gait pattern assessed at a constant, sub-maximal velocity.     

The effects of hydration status and ice-water dousing on physiological and performance indices during a simulated soccer match in the heat

ObjectivesTo assess the effects of hydration status and ice-water dousing on physiological and performance parameters.DesignRandomized, crossover.MethodsTwelve athletes (mean[M] ± standard deviation[SD]; age, 20 ± 1 years; height, 174 ± 8 cm; body mass, 72.1 ± 11.0 kg; VO_2max 53.9 ± 7.3 mL⋅kg⁻¹⋅min⁻¹) completed four trials (euhydrated without dousing, hypohydrated without dousing, euhydrated with dousing, and hypohydrated with dousing), which involved intermittent treadmill running (five 15-minute bouts) in the heat (M ± SD; ambient temperature, 34.7 ± 2.1 °C; relative humidity, 46 ± 3%; wet-bulb globe temperature, 28.0 ± 0.4 °C). Participants also completed four cognitive, power, agility, reaction time, and repeated sprint performance tests throughout each trial. Heart rate (HR) and rectal temperature (T_rec) were measured continuously. Repeated measures ANOVAs were performed to assess differences between physiological and performance variables. Alpha was set at ≤0.05, a priori. Data are reported as mean difference ± standard error (MD ± SE).ResultsHR was significantly lower in euhydrated trials compared to hypohydrated trials, irrespective of dousing (8 ± 2 bpm; p = 0.001). Dousing did not significantly impact HR (p = 0.455) and there was no interaction between hydration and dousing (p = 0.893). T_rec was significantly lower in euhydrated trials compared to hypohydrated trials (0.39 ± 0.05 °C, p < 0.001), with no effect from dousing alone (p = 0.113) or the interaction of hydration and dousing (p = 0.848). Dousing resulted in improved sprint performance (11 ± 3 belt rotations, p = 0.007), while hydration status did not (p = 0.235).ConclusionsAthletes should aim to maintain euhydration during exercise in the heat for improved physiological function and cooling with ice-water dousing elicits additional performance benefits.     

Hot ambient conditions do not alter intermittent cycling sprint performance

ObjectivesTo investigate the effect of hot exposure on the ability to perform intermittent cycling sprints.DesignRepeated measures.MethodsTen male volunteers performed 35 min of intermittent cycling comprising of 8 maximal 6-s sprints interspersed by 1 min of passive recovery followed by 4 min of constant-load pedaling (1 W kg^?1 of body weight) on a cycle ergometer in control (24?C, 24% rH) and hot (40?C, 40% rH) environments.ResultsPeak power output did not decrease during the exercise and was not dependent on the environmental temperature (average of 767 ± 120 W in control and 767 ± 119 W in hot, NS). Skin temperatures (e.g., chest: 36.8 ± 0.8 vs. 32.7 ± 0.6°C), heart rate (132 ± 13 vs. 118 ± 13 bpm) and rating of perceived exertion (13 ± 3 vs. 11 ± 3) were higher (all p < .05) in hot than control environment. However, EMG activity (RMS, vastus lateralis) and neuromuscular efficiency (power/RMS ratio) were similar at the two environmental conditions.ConclusionsDespite higher cardiovascular and perceptual strain in the hot trial, heat exposure did not alter neither peak power output nor related muscle activation and neuromuscular efficiency in the absence of hyperthermia (average core temperature of 37.6 ± 0.3°C in control vs. 37.7 ± 0.4°C in hot, NS).     

Does exertional heat stress impact gastrointestinal function and symptoms?

ObjectivesExertional-heat stress generates a thermoregulatory strain that exacerbates splanchnic hypoperfusion and sympathetic drive, but the effects on gastrointestinal function are poorly defined. The study aimed to determine the effects of exertional-heat stress on gastric myoelectrical activity, orocecal transit time (OCTT), and gastrointestinal symptoms (GIS).DesignRandomised cross-over study.MethodsEndurance runners (n = 16) completed 2 h of running at 60 % V?O_2max in 35 °C (HOT) and 22 °C (TEMP) ambient conditions. Surface electrogastrography (cEGG) was recorded pre- and post-exercise to determine gastric myoelectrical activity, a lactulose challenge was used to determine OCTT, and GIS were recorded using a modified visual analogue scale tool.ResultsPost-exercise T_re [HOT:38.8(38.5 to 39.0)°C and TEMP:38.1(37.8 to 38.4)°C] and Δ T_re [HOT:2.2(2.0 to 2.4)°C and TEMP:1.5(1.2 to 1.8)°C] was higher on HOT compared to TEMP (p < 0.001). Normal gastric myoelectrical cycle frequency reduced (p = 0.010) on HOT [? 11.7(? 20.8 to ? 2.6)%], but this decrease did not differ (p = 0.058) from TEMP [? 2.7(? 8.3 to 3.0)%]. Bradygastria increased post-exercise on both trials (HOT:11.3(2.3 to 20.4)%, p = 0.030; and TEMP:7.4(2.1 to 12.6)%, p = 0.009). OCTT did not differ between trials (p = 0.864) with transit response classified as very slow on both HOT (99(68 to 131)min) and TEMP (98(74 to 121)min). GIS incidence was higher on HOT (88 %) compared to TEMP (81 %), in accordance with greater total-GIS and upper-GIS severity (p = 0.005 and p = 0.033, respectively).ConclusionsRunning for 2 h at 60 % V?O_2max in either hot or temperate ambient conditions instigates perturbations in myoelectrical activity and OCTT, with GIS incidence and severity greater in hot conditions.     

Vascular and oxygenation responses of local ischemia and systemic hypoxia during arm cycling repeated sprints

ObjectivesThe purpose of this study was to investigate the acute vascular and oxygenation responses to repeated sprint exercise during arm cycling with either blood flow restriction (BFR) or systemic hypoxia alone or in combination.DesignThe study design was a single-blinded repeated-measures assessment of four conditions with two levels of normobaric hypoxia (400 m and 3800 m) and two levels of BFR (0% and 45% of total occlusion).MethodsSixteen active participants (eleven men and five women; mean ± SD; 26.4 ± 4.0 years old; 73.8 ± 9.8 kg; 1.79 ± 0.07 m) completed 5 sessions (1 familiarization, 4 conditions). During each test visit, participants performed a repeated sprint arm cycling test to exhaustion (10 s maximal sprints with 20 s recovery until exhaustion) to measure power output, metabolic equivalents, blood flow, as well as oxygenation (near-infrared spectroscopy) of the biceps brachii muscle tissue.ResultsRepeated sprint performance was decreased with both BFR and systemic hypoxia conditions. Greater changes between minimum-maximum of sprints in total hemoglobin concentration (Δ[tHb]) were demonstrated with BFR (400 m, 45% and 3800 m, 45%) than without (400 m, 0% and 3800 m, 0%) (p < 0.001 for both). Additionally, delta tissue saturation index (ΔTSI) decreased more with both BFR conditions than without (p < 0.001 for both). The absolute maximum TSI was progressively reduced with both BFR and systemic hypoxia (p < 0.001).ConclusionsBy combining high-intensity, repeated sprint exercise with BFR and/or systemic hypoxia, there is a robust stimulus detected by increased changes in blood perfusion placed on specific vascular mechanisms, which were more prominent in BFR conditions.     

Does restricting arm motion compromise short sprint running performance?

BackgroundSynchronized arm and leg motion are characteristic of human running. Leg motion is an obvious gait requirement, but arm motion is not, and its functional contribution to running performance is not known. Because arm-leg coupling serves to reduce rotation about the body’s vertical axis, arm motion may be necessary to achieve the body positions that optimize ground force application and performance.Research questionDoes restricting arm motion compromise performance in short sprints?MethodsSprint performance was measured in 17 athletes during normal and restricted arm motion conditions. Restriction was self-imposed via arm folding across the chest with each hand on the opposite shoulder. Track and field (TF, n = 7) and team sport (TS, n = 10) athletes completed habituation and performance test sessions that included six counterbalanced 30 m sprints: three each in normal and restricted arm conditions. TS participants performed standing starts in both conditions. TF participants performed block starts with extended arms for the normal condition and elevated platform support of the elbows for the crossed-arm, restricted condition. Instantaneous velocity was measured throughout each trial using a radar device. Average sprint performance times were compared using a Repeated Measures ANOVA with Tukey post-hoc tests for the entire group and for the TF and TS subgroups.ResultsThe 30 m times were faster for normal vs. restricted arm conditions, but the between-condition difference was only 1.6% overall and < 0.10 s for the entire group (4.82 ± 0.46 s vs. 4.90 ± 0.46 s, respectively; p < 0.001) and both TF (4.55 ± 0.34 vs. 4.63 ± 0.32 s; p < 0.001) and TS subgroups (5.01 ± 0.46 vs. 5.08 ± 0.47 s; p < 0.001).SignificanceOur findings suggest that when arm motion is restricted, compensatory upper body motions can provide the rotational forces needed to offset the lower body angular momentum generated by the swinging legs. We conclude that restricting arm motion compromised short sprint running performance, but only marginally.     

Neuromuscular control and hop performance in youth and adult male and female football players

ObjectivesTo compare neuromuscular control and hop performance between youth and adult male and female football players.DesignCross-sectional study.Participants119 youth players (13–16 years; 68 males) and 88 adult players (17–26 years; 44 males).Main outcome measuresNeuromuscular control assessed with drop vertical jump (DVJ) and tuck jump assessment (TJA). Hop performance assessed with single-leg hop for distance and side hop.ResultsAdult females had smaller normalized knee separation distances (NKSD) during DVJ at initial contact (77.9 ± 18.5 vs. 86.1 ± 11.0, p = 0.010) and at maximum knee flexion (59.7 ± 23.4 vs.74.1 ± 18.1, p = 0.001) compared to youth females. TJA revealed more technique errors in youths compared to adults (males 10 (8–11) vs. 8 (7–10); females 11 (9–12) vs. 9 (8–11), p < 0.05). Youths demonstrated inferior hop performance (males single-leg hop 142 ± 18 vs. 163 ± 17, side hop 41 ± 12 vs. 52 ± 12, p < 0.001; females side hop 32 ± 10 vs. 38 ± 14, p < 0.05).ConclusionsYouth players demonstrated reduced neuromuscular control during TJA and inferior hop performance compared to adult players. Adult female players demonstrated greater knee valgus during DVJ compared to youth female players.     

Concentric not eccentric cycling sprint intervals acutely impair balance and jump performance in healthy active young adults: A randomized controlled cross-over study

IntroductionModerate aerobic, high-intensity and sprint running or cycling training can transiently impair postural control. However, the acute effects of modified sprint interval training (mSIT) at different muscle working modes have not yet been examined. Thus, this study aimed at investigating acute effects of time-matched eccentric (ECC) versus concentric mSIT cycling session (CON) on jumping and functional balance performance.MethodsTwenty-five healthy and active males (30.0 ± 6.0 years; 80.1 ± 9.1 kg; V̇O_2max: 64.2 ± 7.9 mL kg⁻¹ min⁻¹) were enrolled in this acute randomized controlled crossover trial. Counter-Movement-Jump (CMJ) and functional balance testing (Y-Balance-Test composite score [YBT_CS]; Posturomed total distance: Posturomed_TD) were assessed as primary outcomes before, and immediately after cessation of ECC and CON (10 × 10 s maximum sprints and 50 s of active recovery).ResultsA significant mode × time interaction effect for CMJ (F = 9.620, p = 0.005, η_p² = 0.29) was observed. Subsequent post-hoc testing revealed significant moderate reductions in jumping height after CON (0.31 ± 0.06 vs. 0.27 ± 0.06m; p = 0.004, SMD = 0.59), whilst ECC remained unchanged. YBT_CS (mode × time interaction: F = 6.880, p = 0.015, η_p² = 0.22) showed small but significant balance impairments after CON (0.964 ± 0.068 vs. 0.960 ± 0.063 AU; p = 0.009, SMD = 0.28) and did not significantly change after ECC. Although large significant interaction effects (p = 0.029, η_p² = 0.18) were observed for Posturomed_TD, follow up post-hoc testing did not reveal relevant pre-post differences, neither for ECC nor CON.ConclusionBoth functional balance and jumping performance are deteriorated after acute concentric but not eccentric mSIT cycling. Although higher pedal forces at lower perceived efforts and heart rates during eccentric mSIT were observed, it seems that the cardiocirculatory demanding CON session elicited more pronounced balance and jump performance impairments than eccentric cycling.     

Effect of heat exposure on thermoregulation and hockey-specific response time in field hockey goalkeepers

This study examined the thermoregulatory responses in field hockey goalkeepers during games (Part A), and assessed the effect of heat stress on hockey-specific response time (Part B). In Part A, core temperature (T_c), skin temperature (T_sk), body mass, fluid consumption and heart rate (HR) responses of six goalkeepers during two premier level club games in the Western Australian (winter) hockey season were recorded. Part B assessed the same measures, plus a response time test on four goalkeepers playing a simulated game inside a climate chamber in cool (COOL: 20 °C, 40% RH) and hot (HOT: 35 °C, 40% RH) conditions. In Part A, the mean (±SD) T_c and T_sk measured in games was 38.49 ± 0.20 °C and 34.99 ± 0.99 °C, with increases from baseline of 1.34 ± 0.19 °C and 1.08 ± 0.30 °C, respectively. Most of the increase in T_c resulted from the pre-game warm-up. In Part B, T_c and T_sk only increased significantly (p < 0.05) from baseline in the HOT condition (0.62 ± 0.18 °C and 1.61 ± 0.82 °C, respectively). Response time was significantly slower (0.87 ± 0.14 s, p < 0.01) after heat exposure, compared to COOL (0.75 ± 0.15 s), but the number of correct responses was not affected. For optimal performance, careful attention should be given to strategies to limit T_c increases in field hockey goalkeepers during matches.     

Men's lacrosse protective equipment increases strain during exercise in the heat

ObjectivesThe purpose of this study was to determine thermoregulatory and cardiovascular effects of wearing men's lacrosse protective equipment during simulated lacrosse activities in the heat.DesignWe conducted a randomized, controlled, crossover study.MethodsThirteen healthy men (22 ± 3 y, 76.2 ± 8.9 kg, 181 ± 6 cm, 16.06 ± 6.16% body fat) completed two matched exercise trials in the heat (WBGT: 25.5 ± 0.8 °C). In randomized order, participants donned full men's lacrosse equipment (helmet, shoulder/elbow pads, and gloves) in one trial while the other included no equipment. Participants completed a topography body scan to determine specific body surface area covered with equipment. Rectal temperature (T_re), heart rate (HR), and mean weighted skin temperature (T_sk) were measured throughout trials. Whole body sweat rate was assessed for trial comparisons.ResultsThe equipment covered 32.62 ± 2.53% body surface area in our participants. Post-exercise T_re was significantly greater with equipment (39.36 ± 0.04 °C) compared to control (38.98 ± 0.49 °C; p = .007). The overall rate of rise of T_re was significantly greater with equipment (0.043 ± 0.015 °C·min⁻¹) compared to control (0.031 ± 0.008 °Cmin⁻¹; p = .041). Regardless of time point, HR and T_sk were significantly elevated with equipment compared to control trial (p ≤ .026). Sweat rates were elevated with equipment (1.76 ± 0.74 L·h⁻¹) compared to shorts and t-shirt (1.13 ± 0.26 L·h⁻¹), but this difference was not significant (p = .058).ConclusionsOur data indicate impairments in heat dissipation and increased cardiovascular strain imposed by men's lacrosse equipment.     

The influence of different pelvic technical marker sets upon hip kinematics during gait

BackgroundThe pelvis is commonly tracked during three-dimensional motion analysis using markers located on the anterior and posterior superior iliac spines. However, these markers are prone to soft tissue artefact and marker occlusion, highlighting the need for alternative technical marker sets.Research questionHow comparable are hip joint kinematics calculated using two alternative pelvic technical marker sets and a conventionally modelled pelvis?MethodsFourteen participants undertook 3D gait analysis, walking overground at a self-selected pace (1.38 ± 0.14 m·s⁻¹), barefoot. Hip joint kinematics were compared using root mean square error (RMSE) between a conventionally tracked pelvis and two alternative technical marker sets; (1) posterior cluster and (2) additional iliac crest markers.ResultsThe average RMSE in the sagittal, frontal and transverse planes was 2.5° ± 2.8°, 1.6° ± 0.4° and 0.8° ± 0.4°, respectively for the posterior cluster, and 1.3° ± 0.7°, 0.8° ± 0.3° and 1.4° ± 0.5° for the iliac crest marker set. The RMSE was significantly larger for the posterior cluster compared to the iliac crest model in the sagittal (p = .05, d = .28) and frontal planes (p < .001, d = 7.65). In contrast, the RMSE was significantly lower for the posterior cluster in the transverse plane (p = .01, d = -2.85).SignificanceThe findings of this study suggest that either a posterior cluster or additional iliac crest markers offer means of accurately calculating hip joint kinematics within 3° of the conventional pelvic model. Therefore, either technical marker set offers a viable alternative to the conventional pelvic model for calculating hip joint kinematics.     

Does the temperature of water ingested during exertional-heat stress influence gastrointestinal injury,symptoms, and systemic inflammatory profile?

Objectives

The study aimed to determine the effects of temperature of ingested water during exertional-heat stress on gastrointestinal injury, symptoms and systemic inflammatory responses.

Optimal break structures and cooling strategies to mitigate heat stress during a Rugby League match simulation

ObjectivesTo examine, 1) optimal structure of break periods to mitigate physiological heat strain during rugby league play (Stage 1); and ii) effectiveness of three different cooling strategies applied during breaks (Stage 2).DesignCounter-balanced crossover design.MethodsIn 37 °C, 50% RH, 11 males completed six simulated 80-min (two 40-min halves) rugby league matches on a treadmill with different break structures: regular game (RG) (12-min halftime), 1-min or 3-min “quarter-time” breaks halfway through each half with a 12-min halftime break (R1C and R3C), a 20-min halftime break (EH), or 1-min or 3-min quarter-time breaks with a 20-min halftime break (E1C and E3C) [Stage 1]. Nine participants completed Stage 2, which assessed the application of either ice towels (ICE), an electric fan (FAN) or a misting fan (MST) during breaks in the E3C protocol which, in Stage 1, prevailed as the optimal break structure.ResultsStage 1: Irrespective of quarter-time break duration, reductions in rectal temperature (−0.24 °C ± 0.24) and heart rate (−61 ± 10 bpm) during the halftime break were greater with a 20-min compared to a 12-min break (−0.08 ± 0.13 °C, p = 0.005; −55 ± −9 bpm, p = 0.021). Stage 2: End-game rises in rectal temperature were smaller (p < 0.006) in MST (1.41 ± 0.22 °C), FAN (1.55 ± 0.36 °C) and ICE (1.60 ± 0.21 °C) than in CON (1.80 ± 0.39 °C). The end-halftime heart rate was lower (p < 0.001) in ICE (89 ± 13 bpm), MST (90 ± 10 bpm) and FAN (92 ± 13 bpm) than in CON (99 ± 18 bpm).ConclusionsCombining an extended halftime period and quarter-time breaks with MST application is the optimal cooling strategy for rugby league players in hot, humid conditions.     

Morning resistance exercise and cricket-specific repeated sprinting each improve indices of afternoon physical and cognitive performance in professional male cricketers

ObjectivesTo compare two modes (general and cricket-specific) of morning priming exercise on afternoon physical and cognitive performance, and subjective readiness to perform in professional male cricketers.DesignRandomised, crossover, counterbalanced.MethodsOn three occasions, 16 professional men's cricketers completed afternoon tests of countermovement jump height, cricket-specific sprint performance (running between the wickets, two runs), cognitive function (Stroop test, time taken), and subjective readiness to perform. Control (CON; passive rest), lower-body resistance exercise priming (LIFT; trap bar deadlifts, 6 × 4 repetitions up to 85% of one repetition maximum), or cricket-specific running priming (RUN; 6 × 35.36 m sprints including a 180° change of direction) interventions were implemented 5.5 h before testing.ResultsAfternoon sprint times were faster in RUN (?0.04 s, p = 0.013) and LIFT (?0.07 s, p < 0.001) versus CON, and faster in LIFT than RUN (?0.03 s, p = 0.032). Jump height (+1.1 cm, p = 0.021) and cognitive function (?3.83 s, p = 0.003) were greater in LIFT than CON, whilst RUN outperformed CON for cognition (?2.52 s, p = 0.023). Although perceived readiness was not influenced by trial (p > 0.05), players reported favourable responses on the “aggression” subscale in LIFT relative to CON (+1 arbitrary unit, p = 0.022).ConclusionsBoth general (lower-body resistance exercise) and cricket-specific (simulated running between wickets) morning priming are effective match-day strategies to improve afternoon markers of physical and cognitive performance in professional men's cricketers. Practitioners may thus be afforded flexibility in situations where resistance exercise is not feasible on the morning of a match.     

Aptitudes cardiorespiratoires et fonction musculaire périphérique chez des patients coronariens

Objective. – The aim of this study is to determine if the diminished aerobic capacity of coronary artery disease patients is accompanied by a impaired peripheral skeletal muscle function compared to healthy control subjects.Methods. – Thirteen coronary patients and 9 healthy control subjects (57 ± 7 vs 55 ± 8 years) have realised both a maximal laboratory exercise testing and an assessment of the peripheral skeletal muscle function on a isokinetic apparatus (Cybex Norm II). The cardiorespiratory and mechanical parameters (VO₂ uptake, VE, HR and Power output) were measured at ventilatory threshold and maximal effort during a cycloergometer testing. The peripheral skeletal muscle function of the quadriceps was assessed from the maximal voluntary isometric force (MVIF) and from static endurance time (SET) at an intensity of 50% of the MVIF.Results. – Coronary patients showed a diminished aerobic capacity at maximal effort (VO_2max: 23.56 ± 8.1 vs 42.43 ± 9.74 ml min^–1 kg^–1, p < 0.0001; VE_max: 67.07 ± 16.85 vs 90.15 ± 20.76 l min^–1, p < 0.01; HR_max: 110 ± 17 vs 153 ± 20 beats min^–1, p < 0.0001; P_max: 133 ± 40 vs 233 ± 39 W, p < 0,001) but also at ventilatory threshold (VO₂: 15.81 ± 5.7 vs 29.61 ± 7.8 ml min^–1 kg^–1, p < 0.001; HR: 92±11 vs 135±21 beats.min^–1, p < 0.0001, P: 88 ± 32 vs 153 ± 39 W, p < 0.001) except for VE (VE: 38.98 ± 9.91 vs 46.68 ± 7.03 l min^–1, NS). No difference was found between the MVIF (MVIF: 230 ± 46 vs 228 ± 21 N m^–1, NS) between coronary patients and control subjects whereas the SET is lower in coronary patients (65 ± 19 vs 88 ± 9 s, p < 0.003).Conclusion. – Coronary artery disease patients have a lower aerobic capacity accompanied by a impaired peripheral skeletal muscle function.     

Physical fitness and performance. Fatigue responses during repeated sprints matched for initial mechanical output

PURPOSE: To compare muscle fatigability during two sets of repeated cycling sprints matched for initial mechanical output in a nonfatigued and fatigued state. METHODS: Eight young men performed 10, 6-s all-out sprints on a cycle ergometer interspersed with 30 s of recovery, followed, after 6 min of passive recovery, by five 6-s sprints, again interspersed by 30 s of recovery. RESULTS: On the basis of total work (TW), performance in sprint 11 (79.8 +/- 4.8 J.kg) was not significantly different to performance in sprint 4 (80.3 +/- 5.3 J.kg; P = 0.81). The decrease in TW for the five sprints after sprint 4 (i.e., sprints 4 to 8) averaged 14.5% (P < 0.001), which was significantly less than the decrement in TW from sprints 11 to 15 (20.3%; P < 0.05). Despite no significant differences in TW values achieved in sprints 4 and 11, the amplitude of the electromyogram (EMG) signal (i.e., root mean square (RMS)) recorded during sprint 11 (0.398 +/- 0.03 V) was 12.0% lower (P < 0.05) than in sprint 4 (0.452 +/- 0.02 V). In contrast, values of EMG median frequency (MF) recorded during sprint 4 (85.5 +/- 5.5 Hz) and 11 (89.3 +/- 7.2 Hz) were not significantly different (P = 0.33). However, the rate of decrease in EMG activity (i.e., RMS and MF) was similar for the two set of sprints. CONCLUSIONS: These findings suggest that previous fatiguing repeated-sprint exercise, followed by a rest period, induces greater fatigability during subsequent repeated-sprint exercise, regardless of the initial mechanical output, and that these changes are associated with acute neuromuscular adjustments.     

Effect of recovery intensity on peak power output and the development of heat strain during intermittent sprint exercise while under heat stress

This study compared two intensities of active recovery on intermittent sprint exercise performance and the development of heat strain in hot, humid conditions. Eight male game players completed four Cycling Intermittent Sprint Protocols (CISP) consisting of twenty 2-min periods, each including 10-s passive rest, 5-s maximal sprint against a resistance of 7.5% body mass and 105-s active recovery. The CISP was performed in mean (S.D.) temperate conditions with active recovery intensities of 50% (TEMP50) and 35% (TEMP35) and in hot, humid [35.2 (0.4) °C, 80.4 (2.1)% RH] conditions with the same intensities (HOT50 and HOT35, respectively) in a randomised, counterbalanced order. Heat strain (physiological strain index (PSI)) was calculated from rectal temperature and heart rate. All subjects completed the CISP (20 sprints) in TEMP50 and TEMP35. The mean number of sprints completed for HOT50 and HOT35 was 13 (3) and 17 (2), respectively; both of which were lower than TEMP50 and TEMP35 (P < 0.01) and different between hot conditions. Reductions in peak power output (PPO) occurred in the TEMP50 and HOT50 by sprint 8 (P < 0.05), but in HOT35 a reduction was delayed until sprint 13 (P < 0.05). The rate of PSI increase was faster in HOT50 than TEMP50 and HOT35, but peak PSI was not different. By lowering the recovery intensity, one component of the PSI (heart rate) was reduced and intermittent sprint exercise performance was maintained for longer in the heat.     

Juxtametallic Bipolar Bone Radiofrequency Ablation: Thermal Monitoring in an Ex-Vivo Model with Specimen MRI and Histopathologic Correlation

PurposeTo measure the ablation zone temperature and nontarget tissue temperature during radiofrequency (RF) ablation in bone containing metal instrumentation versus no metal instrumentation (control group).Materials and MethodsEx vivo experiments were performed on 15 swine vertebrae (control, n = 5; titanium screw, n = 5; stainless steel screw, n = 5). Screws and RF ablation probe were inserted identically under fluoroscopy. During RF ablation (3 W, 5 minutes), temperature was measured 10 mm from RF ablation centerpoint and in muscle contacting the screw. Magnetic resonance (MR) imaging, gross pathologic, and histopathologic analyses were performed on 1 specimen from each group.ResultsAblation zone temperatures at 2.5 and 5 minutes increased by 12.2 °C ± 2.6 °C and 21.5 °C ± 2.1 °C (control); 11.0 °C ± 4.1 °C and 20.0 °C ± 2.9 °C (juxta-titanium screw), and 10.0 °C ± 3.4 °C and 17.2 °C ± 3.5 °C (juxta–stainless steel) screw; differences among groups did not reach significance by analysis of variance (P = .87). Mixed-effects linear regression revealed a statistically significant increase in temperature over time in all 3 groups (4.2 °C/min ± 0.4 °C/min, P < .001). Compared with the control, there was no significant difference in the temperature change over time for titanium (?0.3 °C/min ± 0.5 °C/min, P = .53) or steel groups (?0.4 °C/min ± 0.5 °C/min, P = .38). The mean screw temperature at the final time point did not show a statistically significant change compared with baseline in either the titanium group (?1.2 °C ± 2.3 °C, P = .50) or steel group (2.6 °C ± 2.9 °C, P = .11). MR imaging and pathologic analyses revealed homogeneous ablation without sparing of the peri-hardware zones.ConclusionsAdjacent metallic instrumentation did not affect the rate of or absolute increase in temperature in the ablation zone, did not create peri–metallic ablation inhomogeneities, and did not result in significant nontarget heating of muscle tissue in contact with the metal instrumentation.     

Relationships between unilateral horizontal and vertical drop jumps and 20 m sprint performance

ObjectivesThe purpose of this study was to compare the relationships between horizontal (HDJ) and vertical drop jumps (VDJ) to sprint performance.DesignExploratory Study.SettingLaboratory.ParticipantsNineteen male collegiate participants (22.5 ± 3.2 years, 181.1 ± 6.7 cm, 80.3 ± 9.6 kg).Main outcome measuresAll participants performed VDJ and HDJ from a 20 cm height onto an AMTI force platform sampling at 1200 Hz before performing three 20 m sprints. Sprint times (5, 10, 15, 20, 5–10, 10–15, 15–20 m) were measured using a LAVEG speed gun.ResultsAll jump and sprint measures showed excellent within session reliability (ICC: 0.954 to 0.99). Pearson's and Spearman's correlations revealed significant (p < 0.01) moderate to high correlations between jump measures and sprint times (R: −0.665 to −0.769). Stepwise multiple regression revealed jump distance normalised by body height (HDJ) was the best predictor for 10, 20, 5–10, 10–15 and 15–20 m sprint times (R² = 41%–48%).ConclusionsHDJ performance measures provide stronger relationships to sprint performance than VDJ's. Thus, HDJ's should be considered in test batteries to monitor training and rehabilitation for athletes in sprint related sports.