Ricardo Mora-Rodriguez

Fluid and carbohydrate ingestion independently improve performance during 1 h of intense exercise

This study determined the effects of fluid and carbohydrate ingestion on performance, core temperature, and cardiovascular responses during intense exercise lasting 1 h. On four occasions, eight men cycled at 80 +/- 1% (+/- SEM) of VO2max for 50 min followed by a performance test. During exercise, they consumed either a large volume (1330 +/- 60 ml) of a 6% carbohydrate (79 +/- 4 g) solution or water or a small volume (200 +/- 10 ml) of a 40% maltodextrin (79 +/- 4 g) solution or water. These trials were pooled so the effects of fluid replacement (Large FR vs Small FR) and carbohydrate ingestion (CHO vs NO CHO) could be determined. Performance times were 6.5% faster during Large FR than Small FR and 6.3% faster during CHO than NO CHO (P < 0.05). At 50 min, heart rate was 4 +/- 1 b.min-1 lower and esophageal temperature was 0.33 +/- 0.04 degrees C lower during Large FR than Small FR (P < 0.05) but no differences occurred between CHO and NO CHO. In summary, Large FR slightly attenuates the increase in heart rate and core temperature which occurs during Small FR. Both fluid and carbohydrate ingestion equally improve cycling performance and their effects are additive.

Caffeine effects on short-term performance during prolonged exercise in the heat.

PURPOSE To determine the effect of water, carbohydrate, and caffeine ingestion on fatigue during prolonged exercise in the heat. METHODS Seven endurance-trained cyclists (V O2max = 61 +/- 8 mL.kg.min) pedaled for 120 min at 63% V O2max in a hot-dry environment (36 degrees C; 29% humidity), ingesting either no fluid (NF), water (WAT) to replace 97% fluid losses, the same volume of a 6% carbohydrate-electrolyte solution (CES), or each of these treatments along with ingestion of 6 mg of caffeine per kilogram of body weight (NF + CAFF, WAT + CAFF, and CES + CAFF). At regular intervals during exercise, maximal cycling power (PMAX) was measured. Before and after exercise, maximal voluntary contraction (MVC), voluntary activation (VA), and electrically evoked contractile properties of the quadriceps were determined. RESULTS Without fluid replacement (NF and NF + CAFF), subjects were dehydrated by 3.8 +/- 0.3%, and rectal temperature reached 39.4 +/- 0.3 degrees C, while it was maintained at 38.7 +/- 0.3 degrees C in trials with rehydration (P < 0.05). Trials with caffeine ingestion increased PMAX by 3% above trials without caffeine (P < 0.05). MVC reductions after exercise were larger with NF (-11 +/- 5%) than for the rest of the trials (P < 0.05). MVC was reduced in WAT compared with CES + CAFF (-6 +/- 4 vs 2 +/- 4%; P < 0.05). However, NF + CAFF maintained MVC at the level of the CES trial. VA showed the same treatment response pattern as MVC. There were no differences in electrically evoked contractile properties among trials. CONCLUSION During prolonged exercise in the heat, caffeine ingestion (6 mg.kg body weight) maintains MVC and increases PMAX despite dehydration and hyperthermia. When combined with water and carbohydrate, caffeine ingestion increases maximal leg force by increasing VA (i.e., reducing central fatigue).

Caffeine during Exercise in the Heat: Thermoregulation and Fluid-Electrolyte Balance

PURPOSE To investigate the effects of caffeine ingestion on thermoregulation and fluid-electrolyte losses during prolonged exercise in the heat. METHODS Seven endurance-trained ( .VO2max = 61 +/- 8 mL.kg.min) heat-acclimated cyclists pedaled for 120 min at 63% .VO2max in a hot-dry environment (36 degrees C; 29% humidity) on six occasions: 1) without rehydration (NF); 2) rehydrating 97% of sweat losses with water (WAT); 3) rehydrating the same volume with a 6% carbohydrate-electrolytes solution (CES); or combining these treatments with the ingestion of 6 mg caffeine.kg (-1) body weight 45 min before exercise, that is, 4) C(AFF) + NF; 5) C(AFF) + WAT; and 6) C(AFF) + CES. RESULTS Without fluid replacement (NF and C(AFF) + NF), final rectal temperature (T(REC)) reached 39.4 +/- 0.1 degrees C, whereas it remained at 38.7 +/- 0.1 degrees C during WAT (CES and C(AFF)+ WAT; (P < 0.05). Caffeine did not alter heat production, forearm skin blood flow, or sweat rate. However, C(AFF) + CES tended to elevate T(REC) above CES alone (38.9 +/- 0.1 degrees C vs 38.6 +/- 0.1 degrees C; P = 0.07). Caffeine ingestion increased sweat losses of sodium, chloride, and potassium ( approximately 14%; P < 0.05) and enlarged urine flow (28%; P < 0.05). CONCLUSION Caffeine ingested alone or in combination with water or a sports drink was not thermogenic or impaired heat dissipation. However, C(AFF) + CES tended to have a higher T(REC) than CES alone. Caffeine increased urine flow and sweat electrolyte excretion, but these effects are not enough to affect dehydration or blood electrolyte levels when exercising for 120 min in a hot environment.

Caffeine Ingestion Reverses the Circadian Rhythm Effects on Neuromuscular Performance in Highly Resistance-Trained Men

Purpose To investigate whether caffeine ingestion counteracts the morning reduction in neuromuscular performance associated with the circadian rhythm pattern. Methods Twelve highly resistance-trained men underwent a battery of neuromuscular tests under three different conditions; i) morning (10:00 a.m.) with caffeine ingestion (i.e., 3 mg kg−1; AMCAFF trial); ii) morning (10:00 a.m.) with placebo ingestion (AMPLAC trial); and iii) afternoon (18:00 p.m.) with placebo ingestion (PMPLAC trial). A randomized, double-blind, crossover, placebo controlled experimental design was used, with all subjects serving as their own controls. The neuromuscular test battery consisted in the measurement of bar displacement velocity during free-weight full-squat (SQ) and bench press (BP) exercises against loads that elicit maximum strength (75% 1RM load) and muscle power adaptations (1 m s−1 load). Isometric maximum voluntary contraction (MVCLEG) and isometric electrically evoked strength of the right knee (EVOKLEG) were measured to identify caffeines action mechanisms. Steroid hormone levels (serum testosterone, cortisol and growth hormone) were evaluated at the beginning of each trial (PRE). In addition, plasma norepinephrine (NE) and epinephrine were measured PRE and at the end of each trial following a standardized intense (85% 1RM) 6 repetitions bout of SQ (POST). Results In the PMPLAC trial, dynamic muscle strength and power output were significantly enhanced compared with AMPLAC treatment (3.0%–7.5%; p≤0.05). During AMCAFF trial, muscle strength and power output increased above AMPLAC levels (4.6%–5.7%; p≤0.05) except for BP velocity with 1 m s−1 load (p = 0.06). During AMCAFF, EVOKLEG and NE (a surrogate of maximal muscle sympathetic nerve activation) were increased above AMPLAC trial (14.6% and 96.8% respectively; p≤0.05). Conclusions These results indicate that caffeine ingestion reverses the morning neuromuscular declines in highly resistance-trained men, raising performance to the levels of the afternoon trial. Our electrical stimulation data, along with the NE values, suggest that caffeine increases neuromuscular performance having a direct effect in the muscle.

Thermoregulatory responses to constant versus variable-intensity exercise in the heat.

PURPOSE To compare the thermoregulatory responses between constant (CON) and variable-intensity exercise (VAR) in a dry-hot environment (36 degrees C, 29% relative humidity, and 2.5 m x s(-1) airflow). METHODS In a random order, seven endurance-trained, heat-acclimated subjects cycled either at 60% VO2max (CON) or alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR). Total work output (915 +/- 100 kJ) and exercise duration (90 min) were identical in both trials. RESULTS Net metabolic heat production was not different between trials (394 +/- 12 vs 408+/- 11 W x m(-2) for VAR vs CON). However, heat storage (60 +/- 3 vs 48 +/- 4 W x m(-2)), the increase in rectal temperature (1.6 +/- 0.1 vs 1.3 +/- 0.1 degrees C), and final heart rate (HR; 147 +/- 5 vs 141 +/- 4 beats x min(-1)) were all higher for VAR than for CON (P < 0.05). During VAR, averaged forearm skin blood flow (S(K)BF) was lower, whereas whole-body sweat rate (1.23 +/- 0.1 vs 1.11 +/- 0.1 L x h(-1)) and dehydration (2.8 +/- 0.1% vs 2.5 +/- 0.2%) were higher than during CON (P < 0.05). Final blood lactate during VAR was higher than during CON (3.5+/- 0.4 vs 2.1 +/- 0.3 mmol x L(-1); P < 0.05). CONCLUSION Ninety minutes of variable-intensity exercise in a hot environment increases heat storage and fluid deficit in comparison to the same amount of work performed in a constant-load mode. VAR increases not only thermal (i.e., heat storage) but also cardiovascular (i.e., heart rate) and metabolic (i.e., blood lactate) stresses, which makes it less advisable than CON when the goal is to minimize physiological stress.

Neuromuscular responses to incremental caffeine doses: performance and side effects.

PURPOSE The purpose of this study was to determine the oral dose of caffeine needed to increase muscle force and power output during all-out single multijoint movements. METHODS Thirteen resistance-trained men underwent a battery of muscle strength and power tests in a randomized, double-blind, crossover design, under four different conditions: (a) placebo ingestion (PLAC) or with caffeine ingestion at doses of (b) 3 mg · kg(-1) body weight (CAFF 3mg), (c) 6 mg · kg(-1) (CAFF 6mg), and (d) 9 mg · kg(-1) (CAFF 9mg). The muscle strength and power tests consisted in the measurement of bar displacement velocity and muscle power output during free-weight full-squat (SQ) and bench press (BP) exercises against four incremental loads (25%, 50%, 75%, and 90% one-repetition maximum [1RM]). Cycling peak power output was measured using a 4-s inertial load test. Caffeine side effects were evaluated at the end of each trial and 24 h later. RESULTS Mean propulsive velocity at light loads (25%-50% 1RM) increased significantly above PLAC for all caffeine doses (5.4%-8.5%, P = 0.039-0.003). At the medium load (75% 1RM), CAFF 3mg did not improve SQ or BP muscle power or BP velocity. CAFF 9mg was needed to enhance BP velocity and SQ power at the heaviest load (90% 1RM) and cycling peak power output (6.8%-11.7%, P = 0.03-0.05). The CAFF 9mg trial drastically increased the frequency of the adverse side effects (15%-62%). CONCLUSIONS The ergogenic dose of caffeine required to enhance neuromuscular performance during a single all-out contraction depends on the magnitude of load used. A dose of 3 mg · kg(-1) is enough to improve high-velocity muscle actions against low loads, whereas a higher caffeine dose (9 mg · kg(-1)) is necessary against high loads, despite the appearance of adverse side effects.

Anaerobic performance when rehydrating with water or commercially available sports drinks during prolonged exercise in the heat

The effects that rehydrating drinks ingested during exercise may have on anaerobic exercise performance are unclear. This study aimed to determine which of four commercial rehydrating drinks better maintains leg power and force during prolonged cycling in the heat. Seven endurance-trained and heat-acclimatized cyclists pedaled for 120 min at 63% maximum oxygen consumption in a hot, dry environment (36 degrees C; 29% humidity, 1.9 m.s-1 airflow). In five randomized trials, during exercise, subjects drank 2.4 +/- 0.1 L of (i) mineral water (WAT; San Benedetto), (ii) 6% carbohydrate-electrolyte solution (Gatorade lemon), (iii) 8% carbohydrate-electrolyte solution (Powerade Citrus Charge), (iv) 8% carbohydrate-electrolyte solution with lower sodium concentration than other sports drinks (Aquarius orange), or (v) did not ingest any fluid (DEH). Fluid balance, rectal temperature (Trec), maximal cycling power (Pmax), and leg maximal voluntary isometric contraction (MVC) were measured. During DEH, subjects lost 3.7 +/- 0.2% of initial body mass, whereas subjects lost only 0.8% +/- 0.1% in the other trials (p < 0.05). Final Trec was higher in DEH than in the rest of the trials (39.4 +/- 0.1 degrees C vs. 38.7 +/- 0.1 degrees C; p < 0.05). Pmax was similar among all trials. Gatorade and Powerade preserved MVC better than DEH (-3.1% +/- 2% and -3.8% +/- 2% vs. -11% +/- 2%, p < 0.05), respectively, whereas WAT and Aquarius did not (-6% +/- 2%). Compared with DEH, rehydration with commercially available sports drinks during prolonged exercise in the heat preserves leg force, whereas rehydrating with water does not. However, low sodium concentration in a sports drink seems to preclude its ergogenic effects on force.

Obesity as a mediator of the influence of cardiorespiratory fitness on cardiometabolic risk: a mediation analysis.

OBJECTIVE The relationship between cardiorespiratory fitness (CRF) and metabolic syndrome (MetS) is well known, although the extent to which body weight may act as a confounder or mediator in this relationship is uncertain. The aim of this study was to examine whether the association between CRF and cardiometabolic risk factors is mediated by BMI. RESEARCH DESIGN AND METHODS A cross-sectional study including 1,158 schoolchildren aged 8–11 years from the province of Cuenca, Spain, was undertaken. We measured height, weight, waist circumference (WC), blood pressure, fasting plasma lipid profile and insulin, and CRF (20-m shuttle run test). A validated cardiometabolic risk index was estimated by summing standardized z scores of WC, log triglyceride-to-HDL cholesterol ratio (TG/HDL-c), mean arterial pressure (MAP), and log fasting insulin. To assess whether the association between CRF and cardiometabolic risk was mediated by BMI, linear regression models were fitted according to Baron and Kenny procedures for mediation analysis. RESULTS In girls, BMI acts as a full mediator in the relationship between CRF and cardiometabolic risk factors, with the exception of log TG/HDL-c ratio. In boys, BMI acts as a full mediator in the relationship between CRF and both log TG/HDL-c ratio and MAP, and as a partial mediator in the relationship between CRF and cardiometabolic risk factors. CONCLUSIONS BMI mediates the association between CRF and MetS in schoolchildren. Overall, good levels of CRF are associated with lower cardiometabolic risk, particularly when accompanied by weight reduction.

Imposing a pause between the eccentric and concentric phases increases the reliability of isoinertial strength assessments

Abstract This study analysed the effect of imposing a pause between the eccentric and concentric phases on the biological within-subject variation of velocity- and power–load isoinertial assessments. Seventeen resistance-trained athletes undertook a progressive loading test in the bench press (BP) and squat (SQ) exercises. Two trials at each load up to the one-repetition maximum (1RM) were performed using 2 techniques executed in random order: with (stop) and without (standard) a 2-s pause between the eccentric and concentric phases of each repetition. The stop technique resulted in a significantly lower coefficient of variation for the whole load–velocity relationship compared to the standard one, in both BP (2.9% vs. 4.1%; P = 0.02) and SQ (2.9% vs. 3.9%; P = 0.01). Test–retest intraclass correlation coefficients (ICCs) were r = 0.61–0.98 for the standard and r = 0.76–0.98 for the stop technique. Bland–Altman analysis showed that the error associated with the standard technique was 37.9% (BP) and 57.5% higher (SQ) than that associated with the stop technique. The biological within-subject variation is significantly reduced when a pause is imposed between the eccentric and concentric phases. Other relevant variables associated to the load–velocity and load–power relationships such as the contribution of the propulsive phase and the load that maximises power output remained basically unchanged.

Improvements on neuromuscular performance with caffeine ingestion depend on the time-of-day

OBJECTIVES To determine whether the ergogenic effects of caffeine ingestion on neuromuscular performance are similar when ingestion takes place in the morning and in the afternoon. DESIGN Double blind, cross-over, randomized, placebo controlled design. METHODS Thirteen resistance-trained males carried out bench press and full squat exercises against four incremental loads (25%, 50%, 75% and 90% 1RM), at maximal velocity. Trials took place 60 min after ingesting either 6 mg kg(-1) of caffeine or placebo. Two trials took place in the morning (AMPLAC and AMCAFF) and two in the afternoon (PMPLAC and PMCAFF), all separated by 36-48 h. Tympanic temperature, plasma caffeine concentration and side-effects were measured. RESULTS Plasma caffeine increased similarly during AMCAFF and PMCAFF. Tympanic temperature was lower in the mornings without caffeine effects (36.7±0.4 vs. 37.0±0.5°C for AM vs. PM; p<0.05). AMCAFF increased propulsive velocity above AMPLAC to levels similar to those found in the PM trials for the 25%, 50%, 75% 1RM loads in the SQ exercise (5.4-8.1%; p<0.05). However, in the PM trials, caffeine ingestion did not improve propulsive velocity at any load during BP or SQ. The negative side effects of caffeine were more prevalent in the afternoon trials (13 vs. 26%). CONCLUSIONS The ingestion of a moderate dose of caffeine counteracts the muscle contraction velocity declines observed in the morning against a wide range of loads. Caffeine effects are more evident in the lower body musculature. Evening caffeine ingestion not only has little effect on neuromuscular performance, but increases the rate of negative side-effects reported.