J C. Boyd

Comparison of glycerol and water hydration regimens on tennis-related performance.

PURPOSE To compare glycerol and water hyperhydration and rehydration on tennis related skill and agility performance. METHODS Eleven male subjects completed two counter-balanced, double-blind trials. Each trial consisted of three phases: 1). hyperhydration with or without glycerol (1.0 g.kg/(-1)) over 150 min, 2). 120 min of exercise-induced dehydration (EID), and 3) rehydration with or without glycerol (0.5 g.kg(-1)) over 90 min. After each phase, subjects performed 5- and 10-m sprint tests, a repeated-effort agility test, and tennis skill tests. RESULTS Glycerol (G) hyperhydration significantly increased fluid retention by approximately 900 mL over the placebo (P) (P<or= 0.05). After EID, body weight was reduced in both groups but was not significantly different between groups (G: -2.71 +/- 0.08, P: -2.67 +/- 0.09%). At the end of the rehydration phase, PV was significantly greater in the G trial than in the P trial, and the G trial resulted in a significantly greater fluid retention of approximately 700 mL over the P trial ( P<or= 0.05). Although the magnitude of hypohydration was modest (<3%), sprint times were significantly slower after the EID ( P<or= 0.05) compared with post hyperhydration and post rehydration but were not significantly different between trials. No significant difference existed between groups and across time for the repeated effort agility tests and groundstrokes and serve tests. CONCLUSION The data demonstrate that relatively modest hypohydration ( approximately 2.7%) as a result of EID, significantly slows 5- and 10-m sprint times. Furthermore, although the glycerol hydration regimen provided a better hydration status than the placebo hydration regimen, no performance benefits were observed.

Effect of moderate dehydration on torque, electromyography, and mechanomyography

The purpose of the present investigation was to test the hypotheses that the mechanomyographic (MMG) signal would be affected by hydration status due to changes in the intra‐ and extracellular fluid content (which could affect the degree of fluid turbulence), changes in the filtering properties of the tissues between the MMG sensor and muscle, and changes in torque production that may accompany dehydration. Ten subjects (age 22.5 ± 1.6 years) were tested for maximal isometric (MVC), submaximal isometric (25, 50, and 75%MVC), and maximal concentric isokinetic muscle strength of the biceps brachii in either a euhydrated or dehydrated state while the electromyographic (EMG) and MMG signals were recorded. Separate three‐way and two‐way ANOVAs indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF with dehydration. The lack of dehydration effect suggests that MMG may be more reflective of the intrinsic contractile processes of a muscle fiber (torque production) or the motor control mechanisms (reflected by the EMG) than the tissues and fluids surrounding the muscle fiber.

The effect of glycerol on torque, electromyography, and mechanomyography.

The purpose of this investigation was to determine the effect of hyperhydration on the electromyographic (EMG) and mechanomyographic (MMG) responses during isometric and isokinetic muscle actions of the biceps brachii. Eight (22.1 ± 1.8 years, 79.5 ± 22.8 kg) subjects were tested for maximal isometric, submaximal isometric, and maximal concentric isokinetic muscle strength in either a control (C) or hyperhydrated (H) state induced by glycerol ingestion while the EMG and MMG signals were recorded. Although fluid retention was significantly greater during the H protocol, the analyses indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, or MMG MPF with hyper-hydration. These results indicated that glycerol-induced fluid retention does not affect the torque-producing capabilities of a muscle, the impulses (EMG) going to a muscle, or muscular vibrations (MMG). It has been suggested that EMG and MMG can be used as direct electrical/mechanical monitoring, which could be presented to trainers and athletes; however, before determining the utility of these signals, the MMG and EMG responses should be examined under a variety of conditions such as in the present study.

Post-Exercise Blood Lactate Decline After Training In Competitive Cyclists and Triathletes

The measurement of maximal aerobic capacity (VO2max) is considered one of the best methods to estimate endurance performance. However, other investigators have suggested that the blood lactate response to submaximal exercise may also provide an index of endurance performance (Coyle et al., 1991; Yoshida et al., 1990). Specifically, the power output, oxygen uptake (VO2) and percentage of VO2max associated with the lactate threshold (VO2 LT) have shown to be valid predictors of endurance performance. Endurance training lowers blood lactate concentrations during submaximal exercise at both relative and absolute work rates (Hurley et al., 1984; Westgarth-Taylor et al., 1997). It has been suggested that the lower blood lactate concentrations seen with training may be due, in part, to a greater rate of removal (Donovan & Brooks, 1983; Donovan & Pagliassotti, 1989, 1990). Based on this evidence, it has been postulated that measuring postexercise blood lactate decline may also provide an index of training status and/or capacity for endurance exercise performance. This concept has recently gained popularity, as evidenced by coaches and athletes who use measures of postexercise blood lactate to evaluate fitness and progress in endurance training programs. Despite this increase in popularity, conclusive evidence has yet to be presented regarding the use of postexercise blood lactate measures as an index of training status. The rate of postexercise blood lactate decline has become more pronounced after training in runners when compared to that of untrained individuals during passive recovery (Bonen & Belcastro, 1976). In contrast, other studies have concluded that endurance training had no effect on postexercise blood lactate decline (Bassett, Merrill, Nagle, Agre, & Sampedro, 1991; Evans & Cureton, 1983; Mayes, Hardman, & Williams, 1987). While the measures of the blood lactate response to submaximal exercise have been established as valid indexes of the capacity for aerobic endurance performance, these tests may not always be practical and facilities for testing may not be available. However, measuring postexercise blood lactate decline has become relatively less complicated due to the advent of hand-held blood lactate analyzers. Therefore, the purposes of this investigation were to: (a) determine the effect of a self-implemented cycle training program on measures of postexercise blood lactate decline after training and (b) examine relationships between measures of postexercise blood lactate decline and time trial performance in a group of competitive cyclists and triathletes. Post-Exercise Blood Lactate Decline After Training in Competitive Cyclists and Triathletes Research Note—Physio ogy