Effects of menthol application on the skin during prolonged immersion in swimmers and controls

We hypothesized that menthol application on the skin would enhance vasoconstriction of subjects immersed in cool water, which would reduce heat loss and rectal temperature (Tre) cooling rate. Furthermore, it was hypothesized that this effect would be greater in individuals acclimatized to immersion in 24 °C water, such as swimmers. Seven swimmers (SW) and seven physical education students (CON) cycled at 60% VO₂ max until Tre attained 38 °C, and were then immediately immersed in stirred water maintained at 24 °C on two occasions: without (NM) and with (M; 4.6 g per 100 mL of water) whole‐body skin application of menthol cream. Heart rate, Tre, proximal–distal skin temperature gradient, oxygen uptake (VO₂), electromyographic activity (EMG), and thermal sensation were measured. Tre reduction was similar among SW and CON in NM and CON in M (?0.71±0.31 °C in average), while it was smaller for SW in M (?0.37±0.18 °C, P < 0.01). VO₂ and heart rate were greater in M compared with NM condition (P = 0.01). SW in M exhibited a shift of the threshold for shivering, as reflected in increased VO₂ and EMG activity, toward a higher Tre compared with the other trials. Menthol application on the skin before immersion reduces heat loss, but defends Tre decline more effectively in swimmers than in non‐swimmers.     

Effects of capsaicin application on the skin during resting exposure to temperate and warm conditions

We investigated thermoregulatory and cardiovascular responses at rest in a temperate (20°C) and in a warm (30°C) environment (40% RH) without and with the application of capsaicin on the skin. We hypothesized that regardless of environmental temperature, capsaicin application would stimulate heat loss and concomitantly deactivate heat conservation mechanisms, thus resulting in rectal temperature (Tre) and mean blood pressure decline due to excitation of heat‐sensitive TRPV1. Ten male subjects were exposed, while seated, for 30 minutes to 20.8 ± 1.0°C or to 30.6 ± 1.1°C: without (NCA) and with (CA) application of capsaicin patches on the skin. Thermoregulatory (Tre, proximal‐distal skin temperature gradient) and cardiovascular variables (modelflow technique) as well as oxygen uptake were continuously measured. The area under the curve for Tre decline at 20°C was smaller in CA (?2.1 ± 1.3 a.u.) than in NCA (?0.6 ± 1.1 a.u., P < 0.01, r = 0.8). Likewise, at 30°C it was smaller in CA (?2.2 ± 2.1 a.u.) compared to NCA (?0.8 ± 2.0 a.u., P = 0.02, r = 0.7). Local vasomotor tone and oxygen uptake, were significantly lower by 36.7% ± 94.2% and 12.3% ± 12.3%, respectively, with capsaicin compared to NCA (P = 0.05 and P < 0.01, respectively). Additionally, in 30°C CA mean arterial pressure was lower by 10.7% ± 5.9%, 8.9% ± 5.9%, and 10.6% ± 7.0% compared to 30°C NCA, 20°C NCA, and 20°C CA, respectively (P < 0.01, P = 0.02, and P < 0.01, respectively, d = 1.4‐1.8). In conclusion, capsaicin application on the skin induced vasodilation and Tre decline. At 30°C CA, thermal responses were accompanied by arterial hypotension most likely due to the interactive effects of both stressors (warm environment and capsaicin) on cutaneous vascular regulation.     

Cryotherapy induces an increase in muscle stiffness

Although cold application (ie, cryotherapy) may be useful to treat sports injuries and to prevent muscle damage, it is unclear whether it has adverse effects on muscle mechanical properties. This study aimed to determine the effect of air‐pulsed cryotherapy on muscle stiffness estimated using ultrasound shear wave elastography. Myoelectrical activity, ankle passive torque, shear modulus (an index of stiffness), and muscle temperature of the gastrocnemius medialis were measured before, during an air‐pulsed cryotherapy (−30°C) treatment of four sets of 4 minutes with 1‐minute recovery in between and during a 40 minutes postcryotherapy period. Muscle temperature significantly decreased after the second set of treatment (10 minutes: 32.3±2.5°C; P <.001), peaked at 29 minutes (27.9±2.2°C; P <.001) and remained below baseline values at 60 minutes (29.5±2.0°C; P <.001). Shear modulus increased by +11.5±11.8% after the second set (10 minutes; P =.011), peaked at 30 minutes (+34.7±42.6%; P <.001), and remained elevated until the end of the post‐treatment period (+25.4±17.1%; P <.001). These findings provide evidence that cryotherapy induces an increase in muscle stiffness. This acute change in muscle mechanical properties may lower the amount of stretch that the muscle tissue is able to sustain without subsequent injury. This should be considered when using cryotherapy in athletic practice.     

Cold‐water or partial‐body cryotherapy? Comparison of physiological responses and recovery following muscle damage

The aim of this study is to compare (a) the physiological responses following cold‐water immersion (CWI ) and partial‐body cryotherapy (PBC ) and (b) the effects on recovery following a muscle‐damaging protocol (5 × 20 drop jumps). Nineteen healthy males were randomly allocated into either a CWI (10°C for 10 minutes; n = 9) or a PBC (−60°C for 30 seconds, −135°C for 2 minutes; n = 10) group. The physiological variables (thigh muscle oxygen saturation [SmO₂], cutaneous vascular conductance [CVC ], mean arterial pressure [MAP ], and local skin temperature) were assessed immediately prior and up to 60 minutes post‐treatment (10‐minutes intervals). The recovery variables (thigh muscle swelling, maximum voluntary contraction [MVC ] of the right knee extensors, vertical jump performance [VJP ], and delayed onset of muscle soreness [DOMS ]) were measured immediately prior and up to 72 hours post‐treatment (24‐hours intervals). Compared to PBC values, CVC (at 30 minutes), SmO₂ (at 40 minutes), and lower extremity skin temperature (thigh/shin at 60 minutes) were significantly reduced in the CWI group after the treatment (all P  < .05). Only lower extremity skin temperature was significantly reduced in the PBC group directly post‐treatment (all P  < .05). MAP significantly increased in both groups after the treatments (both P  < .05). DOMS did not differ between groups. MVC and VJP returned to baseline in both groups after 24 hours (P  > .05). CWI had a greater impact on the physiological response compared to PBC . However, both treatments resulted in similar recovery profiles during a 72‐hours follow‐up period.     

Physical and perceptual cooling: Improving cognitive function,mood disturbance and time to fatigue in the heat

This study investigated the effects of menthol swilling and crushed ice ingestion on cognitive function, total mood disturbance (TMD), and time to fatigue (TTF). Twelve male long-distance runners completed three counterbalanced running trials (3 × 30 minutes at 65% VO_2peak and a TTF run at 100% VO_2peak) in hot, humid conditions (35.3 ± 0.3°C, 59.2 ± 2.5% relative humidity). Trials consisted of precooling with crushed ice ingestion and mid-cooling by menthol swilling (MIX), precooling with water ingestion and mid-cooling by menthol swilling (MENTH), and control (CON). Swilling with either 25 mL of menthol solution or placebo occurred upon entry to the heat, at 15-minute intervals during the run and prior to the TTF run. Core temperature, forehead skin temperature, tympanic temperature, perceived thermal sensation, and TMD were significantly lower with MIX compared with MENTH and CON (P < .05). Thirst was satiated in MIX compared with CON; however, MENTH did not have a significant effect. After 90 minutes of running and post-TTF run, fewer errors occurred in the executive control task (P < .05), as well as decision-making and working memory (P > .05; d = 0.5-0.79) between MIX and CON; however, MENTH had no effect compared with CON. The TTF run was significantly longer with MENTH (34.38%; P = .02) and MIX (39.06%; P = .001) compared with CON, with no difference between MENTH and MIX (P = .618). The physical reduction in core and internal head temperature seen with crushed ice ingestion may lead to improvements in cognitive function; however, both MENTH and MIX were sufficient for improving exercise performance.     

Does water temperature influence the performance of key survival skills?

Aquatic survival skills may be compromised in cold water thereby increasing the likelihood of drowning. This study compared physiological, psychological, and behavioral responses of humans treading water and swimming in cold and temperate water. Thirty‐eight participants were classified as inexperienced (n = 9), recreational (n = 15), or skilled (n = 10) swimmers. They performed 3 tasks: treading water (120 seconds), swim at “comfortable” pace, and swim at “fast” pace in 2 water conditions (28°C vs 10°C). Heart rate, oxygen uptake, psychometric variables, spatio‐temporal (swim speed, stroke rate, and stroke length), and coordination type were examined as a function of expertise. Tasks performed in cold water‐generated higher cardiorespiratory responses (HR  = 145 ± 16 vs 127 ± 21 bpm) and were perceived about 2 points more strenuous on the Borg scale on average (RPE  = 14.9 ± 2.8 vs 13.0 ± 2.0). The voluntary durations of both treading water (60 ± 32 vs 91 ± 33 seconds) and swimming at a comfortable pace (66 ± 22 vs 103 ± 34 seconds) were significantly reduced in cold water. However, no systematic changes in movement pattern type could be determined in either the treading water task or the swimming tasks. Water temperature influences the physical demands of these aquatic skills but not necessarily the behavior. Training treading water and swimming skills in temperate water seems to transfer to cold water, but we recommend training these skills in a range of water conditions to help adapt to the initial “cold‐shock” response.     

Biomechanics of graded running: Part I - Stride parameters,external forces,muscle activations

Biomechanical alterations with graded running have only been partially quantified, and the potential interactions with running speed remain unclear. We measured spatiotemporal parameters, ground reaction forces, and leg muscle activations (EMG) in nineteen adults (10F/9M) running on an instrumented treadmills at 2.50, 3.33, and 4.17 m·s⁻¹ and 0, ±5°, and ±10°. Step frequency illustrated a significant speed × grade interaction (P < .001) and was highest (+3%) at the steepest grade (+10°) and fastest speed (4.17 m·s⁻¹) when compared to level running (LR) at the same speed. Significant interaction was also observed for ground reaction forces (all P ≤ .047). Peak ground reaction forces in the normal direction increased with running speed during downhill running (DR) only (+9% at −10° and 4.17 m·s⁻¹). Impulse in the normal direction decreased at fastest speed and steepest DR (−9%) and uphill running (UR) (−17%) grades. Average normal loading rate increased and decreased at fastest speed and steepest DR (+52%) and UR (−28%) grades, respectively. Negative parallel impulse increased and decreased at fastest speed and steepest DR (+166%) and UR (−90%), respectively. Positive parallel impulse decreased and increased at fastest speed and steepest DR (−75%) and UR (+111%), respectively. EMG showed comparable u-shaped curves across the grades investigated, although only a change in vastus lateralis and tibilias anterior activity was detectable at the steepest grades and fastest speed. Overall, running grade and speed significantly influences spatiotemporal parameters, ground reaction forces, and muscle activations.     

Effects of hydration status during heat acclimation on plasma volume and performance

The impact of hydration status was investigated during a 5‐day heat acclimation (HA) training protocol vs mild/cool control conditions on plasma volume (PV) and performance (20 km time‐trial [TT]). Sub‐elite athletes were allocated to one of two heat training groups (90 min/day): (a) dehydrated to ~2% body weight (BW) loss in heat (35°C; DEH; n = 14); (b) euhydrated heat (35°C; EUH; n = 10), where training was isothermally clamped to 38.5°C core temperature (T_c). A euhydrated mild control group (22°C; CON; n = 9) was later added, with training clamped to the same relative heart rate (~75% HR_max) as elicited during DEH and EUH; thus all groups experienced the same internal training stress (%HR_max). Five‐day total thermal load was 30% greater (P < 0.001) in DEH and EUH vs CON. There were significant differences in the average percentage of maximal work rate (%W_max) across all groups (DEH: 24 ± 6%; EUH: 34 ± 9%; CON: 48 ± 8%W_max) during training required to elicit the same %HR_max (77 ± 4% HR_max). There were no significant differences pre‐to post‐HA between groups for PV (DEH: +1.7 ± 10.1%; EUH: +4.8 ± 10.2%; CON: +5.2 ± 4.0%), but there was a significant pooled group PV increase, as well as a 97% likely pooled improvement in TT performance (DEH: ?1.8 ± 2.8%; EUH: ?1.9 ± 2.1%, CON; ?1.8 ± 2.8%; P = 0.136). Due to a lack of between‐group differences for PV and TT, but pooled group increases in PV and 97% likely group increase in TT performance, over 5 days of intense training at the same average relative cardiac load suggests that overall training stress may also impact significant adaptations beyond heat and hydration stress.     

The use of continuous vs. intermittent cold water immersion as a recovery method in basketball players after training: a randomized controlled trial

Objectives: The main objective of this study was to compare two cold water immersion protocols, continuous or intermittent, on recovery in basketball players.

Methods: Ten male basketball players (age: 14 ± 0.4 years, body mass: 65.4 ± 9.1 kg, height: 175 ± 7.3 cm, body fat %: 10.3 ± 4) were included in the study. After three 90-minute training sessions (avg. heart rate 158 ± 11.92, 156 ± 7.06 and 151 ± 10.44 bpm), participants were grouped into a continuous immersion (12 min at 12 ± 0.4°C) group, intermittent immersion (4 x 2 min immersion at 12 ± 0.4 °C + 1 min out of water) group and a control group (CG). Countermovement jump (CMJ), muscle pain and thigh volume were measured.

Results: Both cold water immersion protocols were effective in reducing the pain 24 and 48 hours after training compared with the CG (F (3.54) = 2.91, p = 0.016, η_p² = .24). Concerning CMJ change, % differences occurred at 24 (Z = 11.04, p = 0.004) and 48 hours (Z = 14.01, p < 0.001) in comparison with the CG. Regarding the muscle volume, the statistical analysis did not report a significant interaction (F (3.54) = 2.42, p = 0.058).

Conclusion: Both cold water immersion CWI protocols are effective in improving recovery in basketball players.     

Running performance and thermal sensation in the heat are improved with menthol mouth rinse but not ice slurry ingestion

The purpose of this study was to compare the effects of a cooling strategy designed to predominately lower thermal state with a strategy designed to lower thermal sensation on endurance running performance and physiology in the heat. Eleven moderately trained male runners completed familiarization and three randomized, crossover 5‐km running time trials on a non‐motorized treadmill in hot conditions (33 °C). The trials included ice slurry ingestion before exercise (ICE), menthol mouth rinse during exercise (MEN), and no intervention (CON). Running performance was significantly improved with MEN (25.3 ± 3.5 min; P = 0.01), but not ICE (26.3 ± 3.2 min; P = 0.45) when compared with CON (26.0 ± 3.4 min). Rectal temperature was significantly decreased with ICE (by 0.3 ± 0.2 °C; P < 0.01), which persisted for 2 km of the run and MEN significantly decreased perceived thermal sensation (between 4 and 5 km) and ventilation (between 1 and 2 km) during the time trial. End‐exercise blood prolactin concentration was elevated with MEN compared with CON (by 25.1 ± 24.4 ng/mL; P = 0.02). The data demonstrate that a change in the perception of thermal sensation during exercise from menthol mouth rinse was associated with improved endurance running performance in the heat. Ice slurry ingestion reduced core temperature but did not decrease thermal sensation during exercise or improve running performance.     

Effect of high‐intensity resistance circuit‐based training in hypoxia on aerobic performance and repeat sprint ability

Recent acute studies have shown that high‐intensity resistance circuit‐based (HRC ) training in hypoxia increases metabolic stress. However, no intervention studies have yet proven their effectiveness. This study aimed to analyze the effect of 8 weeks of HRC in hypoxia on aerobic performance, resting energy expenditure (REE ), repeat sprint ability (RSA ) and hematological variables. Twenty‐eight subjects were assigned to hypoxia (FiO₂ = 15%; HRC _hyp: n = 15; age: 24.6 ± 6.8 years; height: 177.4 ± 5.9 cm; weight: 74.9 ± 11.5 kg) and normoxia (FiO₂ = 20.9%; HRC _norm: n = 13; age: 23.2 ± 5.2 years; height: 173.4 ± 6.2 cm; weight: 69.4 ± 7.4 kg) groups. Each training session consisted of two blocks of three exercises (Block 1: bench press, leg extension, front pull down; 2: deadlift, elbow flexion, ankle extension). Each exercise was performed at 6 repetitions maximum. Participants exercised twice weekly for 8 weeks and before and after the training program blood test, REE , RSA and treadmill running test were performed. Fatigue index in the RSA test was significantly decreased in the HRC _hyp (−0.9%; P  <  .01; ES  = 2.75) but not in the HRC _norm. No changes were observed in REE and hematological variables. Absolute (4.5%; P  =  .014; ES  = 0.42) and relative (5.2%; P  =  .008; ES  = 0.43) maximal oxygen uptake (VO ₂max), speed at VO ₂max (4%; P  =  .010; ES  =  0.25) and time to exhaustion (4.1%; P  =  .012; ES  =  0.26) were significantly increased in HRC _hyp but not in the HRC _norm. No significant differences between groups were found. Compared with normoxic conditions, 8 weeks of HRC training under hypoxic conditions efficiently improves aerobic performance and RSA without changes in REE and red blood O₂‐carrying capacity.     

Left ventricular biomechanics in professional football players

Chronic exercise induces adaptive changes of left ventricular (LV ) ejection and filling capacities which may be detected by novel speckle‐tracking echocardiography (STE ) and tissue Doppler imaging (TDI )‐based techniques. A total of 103 consecutive male elite Norwegian soccer players and 46 age‐matched healthy controls underwent echocardiography at rest. STE was used to assess LV torsional mechanics and LV systolic longitudinal strain (LS ). Diastolic function was evaluated by trans‐mitral blood flow, mitral annular velocities by TDI , and LV inflow propagation velocity by color M‐mode. Despite similar global LS , players displayed lower basal wall and higher apical wall LS values vs controls, resulting in an incremental base‐to‐apex gradient of LS . Color M‐mode and TDI ‐derived data were similar in both groups. Peak systolic twist rate (TWR ) was significantly lower in players (86.4±2.8 vs controls 101.9±5.2 deg/s, P <.01). Diastolic untwisting rate (UTWR ) was higher in players (−124.5±4.2 vs −106.9±6.7 deg/s) and peaked earlier during the cardiac cycle (112.7±0.8 vs 117.4±2.4% of systole duration, both P <.05). Untwisting/twisting ratio (−1.48±0.05 vs −1.11±0.08; P <.001) and untwisting performance (=UTR /TW ; −9.25±0.34 vs −7.38±0.40 s⁻¹, P <.01) were increased in players. Augmented diastolic wall strain (DWS ), a novel measure of LV compliance in players, was associated with improved myocardial mechanical efficiency. The described myocardial biomechanics may underlie augmented exertional cardiac function in athletes and may have a potential role to characterize athlete′s heart by itself or to distinguish it from hypertensive or hypertrophic cardiomyopathy.     

Partial-body cryotherapy (−135°C) and cold-water immersion (10°C) after muscle damage in females

This randomized controlled trial examined the effects of cold-water immersion (CWI), partial-body cryotherapy (PBC), or a passive control (CON) on physiological and recovery variables following exercise-induced muscle damage (EIMD, 5 × 20 drop jumps) in females. Twenty-eight females were allocated to PBC (30 seconds at −60°C, 2 minutes at −135°C), CWI (10 minutes at 10°C), or CON (10 minutes resting). Muscle oxygen saturation (SmO₂), cutaneous vascular conductance (CVC), mean arterial pressure (MAP), and local skin temperature were assessed at baseline and through 60 minutes (10-minute intervals), while delayed onset of muscle soreness (DOMS), muscle swelling, maximum voluntary isometric contraction (MVIC), and vertical jump performance (VJP) were assessed up to 72 hours (24-hour intervals) following treatments. SmO₂ was lower in PBC (Δ-2.77 ± 13.08%) and CWI (Δ-5.91 ± 11.80%) compared with CON (Δ18.96 ± 1.46%) throughout the 60-minute follow-up period (P < .001). CVC was lower from PBC (92.7 ± 25.0%, 90.5 ± 23.4%) and CWI (90.3 ± 23.5%, 88.1 ± 22.9%) compared with CON (119.0 ± 5.1 and 116.1 ± 6.6%, respectively) between 20 and 30 minutes (P < .05). Mean skin temperature was lower from CWI vs PBC (between 10 and 40 minutes, P < .05). Mean skin temperature was higher in CON compared with CWI up to 60 minutes and compared with PBC up to 30 minutes (P < .05). DOMS was lower following both PBC and CWI compared with CON through 72-hour (P < .05), with no difference between groups. No main group differences for swelling, MVIC, and VJP were observed. In conclusion, CWI elicited generally greater physiological effects compared with PBC while both interventions were more effective than CON in reducing DOMS in females, but had no effect on functional measures or swelling.     

Energy dissipation differs between females with and without chronic ankle instability

Chronic ankle instability (CAI ) is associated with altered energy dissipation patterns, but comparisons to lateral ankle sprain (LAS ) copers have not been explored. The purpose of this study was to examine differences in relative sagittal plane energy dissipation during a single‐leg landing between female CAI and LAS coper participants. We separated 33 females (23.6 ± 4.6 years, 164.3 ± 6.2 cm, 69.4 ± 13.7 kg) into CAI (n = 17) and LAS coper (n = 16) groups. Participants completed 5 single‐leg landings followed by a 5‐second stabilization. We collected sagittal plane kinematics and joint moments at the ankle, knee, hip, and proximal joints (knee and hip) combined then calculated each joint's energy dissipation at 50, 100, 150, and 200 ms post‐landing. We compared the percentage of total energy dissipated by the ankle, knee, hip, and proximal joints during each interval utilizing independent t tests and Cohen's d effect sizes. Statistical significance was set a priori at P  < .05. The CAI group had lower relative energy dissipation from the ankle at 50 (24.7 ± 11.5% vs 39.2 ± 11.8%, P  < .01, d  =  1.25 [0.47, 1.95]), 100 (66.9 ± 19.4% vs 77.7 ± 6.5%, P  = .04, d  =  0.74 [0.01, 1.42]), and 150 ms (70.7 ± 17.8% vs 81.0 ± 5.7%, P  = .03, d  =  0.77 [0.04, 1.46]) compared to LAS copers. The CAI group had a greater hip contribution through 150 ms (17.9 ± 10.7% vs 11.7 ± 4.4%, P  = .04, d  =‐0.75 [‐1.44, ‐0.03]) and the proximal joints at 50 (75.3 ± 11.5% vs 60.8 ± 11.8%, P  < .01, d  =  ‐1.25 [‐1.96, ‐0.47]), 100 (33.1 ± 19.4% vs 22.3 ± 6.5%, P  = .04, d  =  ‐0.74 [‐1.42, ‐0.01]), and 150 ms (29.3 ± 17.8 vs 19.0 ± 5.7%, P  = .03, d  =‐0.77 [‐1.46, ‐0.04]) compared to LAS copers. Females with CAI may benefit from therapeutic exercises designed to correct a single‐leg energy dissipation strategy that relies less on the ankle joint.     

Left ventricular remodeling in elite and sub-elite road cyclists

Marked adaptation of left ventricular (LV) structure in endurance athletes is well established. However, previous investigations of functional and mechanical adaptation have been contradictory. A lack of clarity in subjects’ athletic performance level may have contributed to these disparate findings. This study aimed to describe structural, functional, and mechanical characteristics of the cyclists’ LV, based on clearly defined performance levels. Male elite cyclists (EC) (n = 69), sub-elite cyclists (SEC) (n = 30), and non-athletes (NA) (n = 46) were comparatively studied using conventional and speckle tracking 2D echocardiography. Dilated eccentric hypertrophy was common in EC (34.7%), but not SEC (3.3%). Chamber concentricity was higher in EC compared to SEC (7.11 ± 1.08 vs 5.85 ± 0.98 g/(mL)^2/3, P < .001). Ejection fraction (EF) was lower in EC compared to NA (57 ± 5% vs 59 ± 4%, P < .05), and reduced EF was observed in a greater proportion of EC (11.6%) compared to SEC (6.7%). Global circumferential strain (GCε) was greater in EC (−18.4 ± 2.4%) and SEC (−19.8 ± 2.7%) compared to NA (−17.2 ± 2.6%) (P < .05 and P < .001). Early diastolic filling was lower in EC compared with SEC (0.72 ± 0.14 vs 0.88 ± 0.12 cm/s, P < .001), as were septal E’ (12 ± 2 vs 15 ± 2 cm/s, P < .001) and lateral E’ (18 ± 4 vs 20 ± 4 cm/s, P < .05). The magnitude of LV structural adaptation was far greater in EC compared with SEC. Increased GCε may represent a compensatory mechanism to maintain stroke volume in the presence of increased chamber volume. Decreased E and E’ velocities may be indicative of a considerable functional reserve in EC.     

Restricting dietary sodium reduces plasma sodium response to exercise in the heat

Exercise‐associated hyponatremia can be life‐threatening. Excessive hypotonic fluid ingestion is the primary etiological factor but does not explain all variability. Possible effects of chronic sodium intake are unknown. The aim of this study was to determine whether dietary sodium affects plasma sodium concentration [Na⁺] during exercise in the heat, when water intake nearly matches mass loss. Endurance‐trained men (n = 9) participated in this crossover experiment. Each followed a low‐sodium (lowNa) or high‐sodium (highNa) diet for 9 days with 24‐h fluid intakes and urine outputs measured before experimental trials (day 10). The trials were ≥2 week apart. Trials comprised 3 h (or if not possible to complete, to exhaustion) cycling (55% VO_2max; 34 °C, 65% RH) with water intake approximating mass loss. Plasma [Na⁺], hematocrit, sweat and urine [Na⁺], heart rate, core temperature, and subjective perceptions were monitored. Urine [Na⁺] was lower on lowNa 24 h prior to (31 ± 24, 76 ± 30 mmol/L, P = 0.027) and during trials (10 ± 10, 52 ± 32 mmol/L, P = 0.004). Body mass was lower on lowNa (79.6 ± 8.5, 80.5 ± 8.9, P = 0.03). Plasma [Na⁺] was lower on lowNa before (137 ± 2, 140 ± 3, P = 0.007) and throughout exercise (P = 0.001). Sweat [Na⁺] was unaffected by diet (54.5 ± 40, 54.5 ± 23 mmol/L, P = 0.99). Heart rate and core temperature were higher on lowNa (P ≤ 0.001). Despite decreased urinary sodium losses, plasma sodium was lower on lowNa, with decreased mass indicating (extracellular) water may have been less, explaining greater heart rate and core temperature. General population health recommendations to lower salt intake may not be appropriate for endurance athletes, particularly those training in the heat.     

Effects of oral rehydration and external cooling on physiology,perception, and performance in hot,dry climates

Only limited research evaluates possible benefits of combined drinking and external cooling (by pouring cold water over the body) during exercise. Therefore, this study examined cold water drinking and external cooling on physiological, perceptual, and performance variables in hot, dry environments. Ten male runners completed four trials of walking 90 min at 30% VO_2max followed by running a 5‐km time trial in 33 ± 1 °C and 30 ± 4% relative humidity. Trials examined no intervention (CON), oral rehydration (OR), external cooling (EC), and oral rehydration plus external cooling (OR + EC). Investigators measured rectal temperature, skin temperatures, heart rate, thirst, thermal sensation, and ratings of perceived exertion (RPE). Oral rehydration (OR and OR + EC) significantly lowered heart rate (P < 0.001) and thirst (P < 0.001) compared with nondrinking (CON and EC) during low‐intensity exercise. External cooling (EC and OR + EC) significantly reduced chest and thigh temperature (P < 0.001), thermal sensation (P < 0.001), and RPE (P = 0.041) compared with non‐external cooling (CON and OR) during low‐intensity exercise. Performance exhibited no differences (CON = 23.86 ± 4.57 min, OR = 22.74 ± 3.20 min, EC = 22.96 ± 3.11 min, OR + EC = 22.64 ± 3.73 min, P = 0.379). Independent of OR, pouring cold water on the body benefited skin temperature, thermal sensation, and RPE during low‐intensity exercise in hot, dry conditions but failed to influence high‐intensity performance.     

Dopamine/noradrenaline reuptake inhibition in women improves endurance exercise performance in the heat

Catecholamine reuptake inhibition improves the performance of male volunteers exercising in warm conditions, but sex differences in thermoregulation, circulating hormones, and central neurotransmission may alter this response. With local ethics committee approval, nine physically active women (mean ± SD age 21 ± 2 years; height 1.68 ± 0.08 m; body mass 64.1 ± 6.0 kg; VO_2peak 51 ± 7 mL/kg/min) were recruited to examine the effect of pre‐exercise administration of Bupropion (BUP; 4 × 150 mg) on prolonged exercise performance in a warm environment. Participants completed a VO_2peak test, two familiarization trials, and two randomized, double‐blind experimental trials. All trials took place during the first 10 days of the follicular phase of the menstrual cycle. Participants cycled for 1 h at 60% VO_2peak followed by a 30‐min performance test. Total work done was greater during the BUP trial (291 ± 48 kJ) than the placebo trial (269 ± 46 kJ, P = 0.042, d = 0.497). At the end of the performance test, core temperature was higher on the BUP trial (39.5 ± 0.4 °C) than on the placebo trial (39.2 ± 0.6 °C, P = 0.021; d = 0.588), as was heart rate (185 ± 9 vs 179 ± 13, P = 0.043; d = 0.537). The results indicate that during the follicular phase of the menstrual cycle, an acute dosing protocol of BUP can improve self‐regulated performance in warm conditions.     

Cold‐water immersion decreases cerebral oxygenation but improves recovery after intermittent‐sprint exercise in the heat

This study examined the effects of post‐exercise cooling on recovery of neuromuscular, physiological, and cerebral hemodynamic responses after intermittent‐sprint exercise in the heat. Nine participants underwent three post‐exercise recovery trials, including a control (CONT), mixed‐method cooling (MIX), and cold‐water immersion (10 °C; CWI). Voluntary force and activation were assessed simultaneously with cerebral oxygenation (near‐infrared spectroscopy) pre‐ and post‐exercise, post‐intervention, and 1‐h and 24‐h post‐exercise. Measures of heart rate, core temperature, skin temperature, muscle damage, and inflammation were also collected. Both cooling interventions reduced heart rate, core, and skin temperature post‐intervention (P < 0.05). CWI hastened the recovery of voluntary force by 12.7 ± 11.7% (mean ± SD) and 16.3 ± 10.5% 1‐h post‐exercise compared to MIX and CONT, respectively (P < 0.01). Voluntary force remained elevated by 16.1 ± 20.5% 24‐h post‐exercise after CWI compared to CONT (P < 0.05). Central activation was increased post‐intervention and 1‐h post‐exercise with CWI compared to CONT (P < 0.05), without differences between conditions 24‐h post‐exercise (P > 0.05). CWI reduced cerebral oxygenation compared to MIX and CONT post‐intervention (P < 0.01). Furthermore, cooling interventions reduced cortisol 1‐h post‐exercise (P < 0.01), although only CWI blunted creatine kinase 24‐h post‐exercise compared to CONT (P < 0.05). Accordingly, improvements in neuromuscular recovery after post‐exercise cooling appear to be disassociated with cerebral oxygenation, rather reflecting reductions in thermoregulatory demands to sustain force production.     

Effects of intense aerobic exercise and/or antihypertensive medication in individuals with metabolic syndrome

We studied the blood pressure lowering effects of a bout of exercise and/or antihypertensive medicine with the goal of studying if exercise could substitute or enhance pharmacologic hypertension treatment. Twenty‐three hypertensive metabolic syndrome patients chronically medicated with angiotensin II receptor 1 blockade antihypertensive medicine underwent 24‐hr monitoring in four separated days in a randomized order; (a) after taking their habitual dose of antihypertensive medicine (AHM trial), (b) substituting their medicine by placebo medicine (PLAC trial), (c) placebo medicine with a morning bout of intense aerobic exercise (PLAC +EXER trial) and (d) combining the exercise and antihypertensive medicine (AHM +EXER trial). We found that in trials with AHM subjects had lower plasma aldosterone/renin activity ratio evidencing treatment compliance. Before exercise, the trials with AHM displayed lower systolic (130 ± 16 vs 133 ± 15 mm Hg; P  = .018) and mean blood pressures (94 ± 11 vs 96 ± 10 mm Hg; P  = .036) than trials with placebo medication. Acutely (ie, 30 min after treatments) combining AHM +EXER lowered systolic blood pressure (SBP ) below the effects of PLAC +EXER (−8.1 ± 1.6 vs −4.9 ± 1.5 mm Hg; P  = .015). Twenty‐four hour monitoring revealed no differences among trials in body motion. However, PLAC +EXER and AHM lowered SBP below PLAC during the first 10 hours, time at which PLAC +EXER effects faded out (ie, at 19 PM ). Adding exercise to medication (ie, AHM +EXER ) resulted in longer reductions in SBP than with exercise alone (PLAC +EXER ). In summary, one bout of intense aerobic exercise in the morning cannot substitute the long‐lasting effects of antihypertensive medicine in lowering blood pressure, but their combination is superior to exercise alone.