Glycerol-induced hyperhydration (GIH) has been shown to improve fluid retention and endurance performance compared with water-induced hyperhydration. The goal of this article is to report on what is known and unknown about how glycerol-containing hyperhydration solutions (GCHSs) are processed at the stomach and intestine level, propose strategies to improve the efficacy of GIH, and provide research questions for future studies. Through statistical analyses, it is demonstrated that the effectiveness of GCHSs in increasing fluid retention is maximized when fluid ingestion is in the upper range of what is normally administered by studies (~26 ml/kg body weight) and the duration of the protocol is no longer than the time it takes for the glycerol-fluid load to be totally or nearly completely integrated inside the body. The rate of gastric emptying and intestinal absorption of GCHSs is unknown. However, based on an analysis of indirect evidence obtained from human studies, it is proposed that most glycerol (~80 g) and fluid (~1,700 ml) ingested during a typical GIH protocol can be integrated inside the body within 60–90 min. Whether the stress associated with competition could alter these figures is unknown. Research in rats indicates that combining glycerol with glucose at a 3:1 ratio accelerates intestinal absorption of both glycerol and water, thereby potentially improving the efficacy of GIH. Human studies must be conducted to determine how GCHSs are processed by the gastrointestinal system and whether adding glucose to GCHSs could improve the technique’s efficacy.
Roy L.P.G. Jentjens and Asker E. Jeukendrup
Vanadium compounds have been shown to have insulin-like properties in rats and non-insulin-dependent diabetic humans. The purpose of the present study was to examine whether the effects of acute and short-term administration of vanadyl sulphate (VS) on insulin sensitivity also exist in healthy active individuals. Five male and 2 female participants (age: 24.9 ± 1.5 years; height: 176.1 ± 2.9 cm; body mass: 70.1 ± 2.9 kg) underwent 3 oral glucose tolerance tests (OGTT). The first OGTT was performed to obtain a baseline index of insulin sensitivity (ISI). On the night preceding the second OGTT, participants ingested 100 mg of VS, and the acute effects of VS on ISI were examined. For the next 6 days, participants were instructed to ingest 50 mg of VS twice daily, and a final OGTT was performed on day 7 to determine the short-term effects of VS on ISI. No differences were found in fasting plasma glucose and insulin concentrations after VS administration. Furthermore, ISI after 1 day and 7 days of VS administration was not different compared with baseline ISI (4.8±0.1 vs. 4.7±0.1 vs. 4.7 ± 0.1, respectively). These results demonstrate that there are no acute and short-term effects of VS administration on insulin sensitivity in healthy humans.
Keitaro Kubo, Hiroaki Kanehisa and Tetsuo Fukunaga
The purposes of this study were to compare the elasticity of tendon and aponeurosis in human knee extensors and ankle plantar flexors in vivo and to examine whether the maximal strain of tendon was correlated to that of aponeurosis. The elongation of tendon and aponeurosis during isometric knee extension (n = 23) and ankle plantar flexion (n = 22), respectively, were determined using a real-time ultrasonic apparatus, while the participants performed ramp isometric contractions up to voluntary maximum. To calculate the strain values from the measured elongation, we measured the respective length of tendon and aponeurosis. For the knee extensors, the maximal strain of aponeurosis (12.1 ± 2.8%) was significantly greater than that of the patella tendon (8.3 ± 2.4%), p < 0.001. On the contrary, the maximal strain of Achilles tendon (5.9 ± 1.4%) was significantly greater than that of aponeurosis in ankle plantar flexors (2.7 ± 1.4%), p < 0.001. Furthermore, for both knee extensors and ankle plantar flexors there was no significant correlation between maximal strain of tendon and aponeurosis. These results would be important for understanding the different roles of tendon and aponeurosis during human movements and for more accurate muscle modeling.
Kevin Deschamps, Giovanni Matricali, Maarten Eerdekens, Sander Wuite, Alberto Leardini and Filip Staes
, Alexander RM . The spring in the arch of the human foot . Nature . 1987 ; 325 ( 6100 ): 147 – 149 . doi:10.1038/325147a0 10.1038/325147a0 3808070 9. Farley CT , Glasheen J , McMahon TA . Running springs: speed and animal size . J Exp Biol . 1993 ; 185 : 71 – 86 . PubMed ID: 8294853 8294853
Alessandra de Carvalho Bastone, Bruno de Souza Moreira, Renata Alvarenga Vieira, Renata Noce Kirkwood, João Marcos Domingues Dias and Rosângela Corrêa Dias
The purpose of this study was to assess the validity of the Human Activity Profile (HAP) by comparing scores with accelerometer data and by objectively testing its cutoff points. This study included 120 older women (age 60–90 years). Average daily time spent in sedentary, moderate, and hard activity; counts; number of steps; and energy expenditure were measured using an accelerometer. Spearman rank order correlations were used to evaluate the correlation between the HAP scores and accelerometer variables. Significant relationships were detected (rho = .47−.75, p < .001), indicating that the HAP estimates physical activity at a group level well; however, scatterplots showed individual errors. Receiver operating characteristic curves were constructed to determine HAP cutoff points on the basis of physical activity level recommendations, and the cutoff points found were similar to the original HAP cutoff points. The HAP is a useful indicator of physical activity levels in older women.
G. Mikael Fogelholm, Hannu K. Näveri, Kai T.K. Kiilavuori and Matti H.A. HärkÖnen
Using a double-blind, crossover protocol, we studied the possible effects of a 4-day combined L-arginine, L-ornithine, and L-lysine supplementation (each 2 g/day, divided into two daily doses) on 24-hr level of serum human growth hormone (hGH) and insulin in 11 competitive weightlifters, ages 19 to 35 yrs. Three similar daily hGH peaks, seemingly preceded by a decrease in serum insulin concentration, were found during both amino acid and placebo supplementation. Supplementation did not affect the physiological variation of serum hGH concentration (treatment and treatment × time interaction: p=0.43–0.55). Analogously, serum insulin levels were not higher after amino acid supplementation. Therefore the ergogenic value of lowdose oral amino acid supplementation in increasing hGH or insulin secretion seems questionable.
Jill L. McNitt-Gray
Using a model for the neuromuscular control of human arm movements, the possible roles of different proprioceptive signals are analyzed. The control model is represented by a neural network and includes both feedback and feedforward control modes. After a learning process, the controller regulates a wide range of arm movements. Evaluation of the roles of different afferent signals shows that sensed muscle forces are important to achieve accurate control of fast movements. For a moderately high loop delay (50 ms), velocity feedback is not essential, but for small loop delays (0 and 25 ms) an increased performance is attained by feedback of velocity. Position sense is essential to prevent steady-state errors. The arm impedance is affected considerably by the delay in the control loop and by the configuration of the motor control system. The achieved relation between muscle length and force is similar to the invariant characteristics laying at the basis of the equilibrium-point (EP) hypothesis. However, control of fast movements on the basis of EP alone is not feasible, but requires feedforward control. During training in a velocity-dependent force field, the impedance of the arm increases at first, due to enhanced cocontraction. Subsequently, both impedance and movement errors decrease, indicating a successful representation of the changed inverse dynamics.
Hermann Zbinden-Foncea, Luc J. C. van Loon, Jean-Marc Raymackers, Marc Francaux and Louise Deldicque
Mitogen-activated protein kinase (MAPK) pathways are activated in skeletal muscle during endurance exercise, but the upstream molecular events are incompletely resolved. As an increase in plasma nonesterified fatty acids (NEFA) is a common feature of long-lasting exercise, the authors tested the hypothesis that NEFA contribute to the activation of MAPK during endurance exercise. Acipimox was used before and during endurance exercise to prevent the elevation of plasma NEFA levels in healthy subjects and patients with diabetes. In 2 separate studies, healthy subjects cycled for 2 hr and patients with diabetes for 1 hr at 50% Wmax. In control conditions, plasma NEFA concentrations increased from 0.35 to 0.90 mM during exercise in healthy subjects and from 0.55 to 0.70 mM in patients with diabetes (p < .05). Phosphorylation states of extracellularly regulated kinase 1 and 2 (ERK1/2), p38, and c-Jun NH2-terminal kinases (JNK) were significantly increased after exercise in the vastus lateralis in both groups. Acipimox blocked the increase in plasma NEFA concentrations and almost completely repressed any rise in ERK1/2 and p38 but not in JNK. In conclusion, the data support a role for plasma NEFA in the activation of p38 and ERK1/2 in skeletal-muscle tissue of healthy and diabetic subjects during endurance exercise. Further investigation will be required to determine the molecular link between NEFA and MAPK activation during exercise in human skeletal muscle.
L.P. Kilduff, E. Georgiades, N. James, R.H. Minnion, M. Mitchell, D. Kingsmore, M. Hadjicharalambous and Y.P. Pitsiladis
The effects of creatine (Cr) supplementation on cardiovascular, metabolic, and thermoregulatory responses, and on the capacity of trained humans to perform prolonged exercise in the heat was examined. Endurance-trained males (n = 21) performed 2 constant-load exercise tests to exhaustion at 63 ± 5 % VO2max in the heat (ambient temperature: 30.3 ± 0.5 °C) before and after 7 d of Cr (20 g · d–1 ’ Cr + 140 g • d–1 glucose polymer) or placebo. Cr increased intraccl-lular water and reduced thermoregulatory and cardiovascular responses (e.g., heart rate, rectal temperature, sweat rate) but did not significantly increase time to exhaustion (47.0 ± 4.7 min vs. 49.7 ± 7.5 min, P = 0.095). Time to exhaustion was increased significantly in subjects whose estimated intramuscular Cr levels were substantially increased (“responders”: 47.3 ± 4.9 min vs. 51.7 ± 7.4 min, P = 0.031). Cr-induced hyperhydration can result in a more efficient thermoregulatory response during prolonged exercise in the heat.