Ergometry for estimation of mechanical power output in sprinting in humans using a newly developed self-driven treadmill

An evaluation of mechanical power during walking and running in humans was undertaken after developing a specially designed running ergometer (RE) in which the subjects gripped the handlebar in front of them keeping both arms straight and in a horizontal position. Ten subjects participated in comparisons of the mean horizontal pushing force (MF _am) on the handlebar with the mean horizontal ground reaction force (MF _fp) recorded by force platform under the RE during five different constant speeds of walking or running and sprint running with maximal effort. Mechanical power developed during sprint running on the RE was compared with a 50 m sprint. Mean linear velocity (Mv) of the RE belt was recorded by the rotary encoder attached to the axis of the belt. Mean mechanical power calculated from the handlebar setting (MP _am=MF _am × Mv) was compared to that calculated from force platform recordings (MP _fp=MF _fp × Mv). A high test-retest reproducibility was observed for both MF _fp (r=0.889) and MF _am (r=0.783). Larger values for the coefficient of variation for MF _am (11.3%–15.8%) were observed than for MF _fp (3.3%–8.2%). The MP _am, which were obtained from five different constant speeds of walking, running and sprint running were closely correlated to those of MP _fp (y=0.98x − 19.10,r=0.982, P < 0.001). In sprint running, MP _am was 521.7 W (7.67 W · kg⁻¹) and was correlated to the 50 m sprint time (r=−0.683, P < 0.01). It is concluded that the newly developed RE was useful in the estimation of mechanical power output during human locomotion such as when walking, jogging and sprinting. Accepted: 10 October 2000     

The effects in humans of rapid loss of body mass on a boxing-related task

The physiological effects of strategies for a rapid loss of body mass immediately before weighing-in for competition in weight-governed sports are unclear. This study examined the effects of a 3%–4% loss in body mass on a boxing-related task. Seven novice amateur boxers completed three 3 min rounds of simulated boxing on a prototype boxing ergometer in an euhydrated state (E-trial) and after exercise-induced thermal dehydration (D-trial). All subjects lost body mass following dehydration–mean body mass fell 3.8 (SD ± 0.3)% [77.3 (SD ± 11.3) to 74.4 (SD ± 10.7) kg, P < 0.001] – but changes in plasma volume (PV) were inconsistent. Four subjects suffered reductions in PV between 15% and 30%, one subject maintained his E-trial value and two recorded an increase. The D-trial mean PV value was 8.0 (SD ± 17.2)% lower but this fall was not statistically significant (P > 0.05). Analysis of D-trial boxing performance showed one subject maintained his performance over the two trials and a second improved 17.8%. A two-way ANOVA (condition × time) with repeated measures on both factors showed no significant main effect differences for condition (F _1,6=3.93 P > 0.05), time (F _1.83,48=1.12, P > 0.05) or interaction between them (F _1.93,48, P > 0.05). Furthermore, neither heart rate nor blood lactate responses in the boxing task differed between trials. These data were affected by the small sample. Power and effect size analysis using η² procedure and removing the outlier data produced a mean fall in boxing performance of 26.8%. However, some subjects appeared able to resist the deleterious effects of a rapid loss of body mass prior to competition and further research is needed to explain the mechanisms under-pinning this ability. Accepted: 12 May 2000     

The effect of selective beta1-blockade on EMG signal characteristics during progressive endurance exercise

This study analysed the effect of selective β₁-blockade on neuromuscular recruitment characteristics during progressive endurance exercise. Ten healthy subjects ingested a selective β₁-blocker, acebutolol (200 mg b.d.), for 7 days (for one of two cycling trials), with a 10-day wash-out period between trials. On the last day of acebutolol ingestion subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak power output and then cycled at increasing (15 W min^–1) work rates to exhaustion. Force output, heart rate, submaximal V˙O₂, rate of perceived exertion (RPE), electromyographic (EMG) data and blood lactate were captured during the cycling activity. Peak work rate [270 (111) W vs 197 (75) W, CON vs BETA, P <0.01], time to exhaustion [49.7 (23.2) min vs 40.3 (23.7) min, CON vs BETA, P <0.05] and heart rate [mean, for the full ride 135.5 (38.3) beats min^–1 vs 111.5 (30.0) beats min^–1 CON vs BETA, P <0.05] were significantly lower for the group who ingested β₁-blockade (BETA) compared to the control group (CON). Although not significant, submaximal V˙O₂ was reduced in BETA during the ride, while RPE was significantly higher during the ride for BETA (P <0.01). Mean integrated electromyography was higher in the BETA group although these differences were not significant. Mean power frequency values of the BETA group showed a significant (P <0.05) shift to the upper end of the spectrum in comparison to the control group. Lactate values [11.7 (3.5) mmol.l^–1 vs 7.1 (4.1) mmol.l^–1 CON vs BETA] were significantly lower (P <0.05) at exhaustion in BETA. Significant reductions in cycling performance were found when subjects ingested β₁-blockers. This study has shown significant shifts to the upper end of the EMG frequency spectrum after β₁-blocker ingestion, which could be caused by a change in neuromuscular recruitment strategy to compensate for the impaired submaximal exercise performance. Electronic Publication     

Prenatal stress during the 1999 bombing associated with lower birth weight—a study of 3,815 births from Belgrade

During the 3-month bombing of Serbia (March 24–June 9, 1999), the entire population, including pregnant females as an especially vulnerable group, was exposed to a high degree of stress. This is the first study to explore the effects of prenatal stress during the 1999 bombing of Belgrade on the main obstetric characteristics of newborns. The design of the study was retrospective cross-sectional. The total number of birth records in the sample was 3,815, namely, 1,198 from the group exposed to prenatal stress and 1,251 and 1,366 from the respective control periods, years 1996 and 2003, when no stressful events affected the city. We found that exposed mothers gave birth to infants with statistically significantly lower birth weight (BW; mean difference = 86 g, 95% confidence interval = 67 to 104; F _{(1, 3,349)} = 80.8, p < 0.001, η _p² = 0.024), when controlling for confounding effects of body length and head circumference. There was no specific relation between the trimester of stress exposure and BW in infants born in 1999. Neither increased frequency of preterm deliveries nor more complications of pregnancy and delivery were found in the given sample. Possible consequences of lower BW on psychosocial and somatic functioning should be evaluated through the lifetime.     

Obesity-dependent association of TNF-LTA locus with type 2 diabetes in North Indians

Six common genetic variants (rs2229094, rs1041981, rs1800630, rs1800629, rs361525, and rs1800610) in the TNF-LTA locus encoding the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and lymphotoxin-α have been shown to be associated with various metabolic traits including susceptibility to type 2 diabetes, metabolic syndrome, insulin resistance, and increased body mass index (BMI) in Caucasians from different geographic locations and have yielded mixed results. We tested for the association of these variants with type 2 diabetes in North Indians by studying 2,115 participants comprising of 1,073 type 2 diabetes patients and 1,042 controls. We report the association of a promoter region variant of TNF: rs1800630 and non-synonymous LTA variant: rs2229094 with type 2 diabetes [OR = 0.83 (95% CI 0.72–0.95), P = 0.005 and OR = 0.86 (95% CI 0.75–0.98), P = 0.02, respectively]. Although these associations were BMI-dependent, no interactive effect of BMI and variants on type 2 diabetes was detectable. Further, the haplotype carrying all the six major alleles conferred susceptibility to type 2 diabetes [OR = 1.23 (95% CI 1.06–1.42), P = 0.005; P _permuted = 0.02], with the effect much enhanced in non-obese subjects [OR = 1.45 (95% CI 1.19–1.78), P = 2 × 10⁻⁴: P _permuted = 3 × 10⁻⁴]. The minor allele of rs2229094 was associated with lower hsCRP, BMI, and waist circumference (WC), while the minor allele of rs1800630 showed association with lower BMI and WC (all P < 0.01). This is the first report demonstrating association of rs1800630 and rs2229094 with type 2 diabetes in any population, suggesting an important role of the TNF-LTA locus in type 2 diabetes in North Indians.     

Substrate utilization in boys during exercise with [13C]-glucose ingestion

The influence of glucose ingestion on substrate utilization during prolonged exercise in children and adolescents is currently unknown. In the present study we determined the effect of intermittent exogenous glucose (GLU_exo) ingestion on substrate utilization during prolonged exercise, in adolescent boys ages 13–17 years. Healthy untrained volunteers performed four 30-min exercise bouts on a cycle ergometer, separated by 5-min rest periods (≅60% maximum O₂ consumption), on two occasions spaced 1–4 weeks apart. Two trials were performed, a control trial (CT), in which subjects ingested water intermittently during the exercise, and a glucose trial (GT), in which subjects ingested a ¹³C-enriched GLU_exo drink (≅3 g glucose · kg body mass⁻¹), also intermittently during the exercise. Total free fatty acids (FAT_total), glucose (GLU_total) and carbohydrate (CHO_total) oxidation was determined from indirect calorimetry, while GLU_exo oxidation was calculated from the ¹³C/¹²C ratio in expired air after 5–10 min and 25–30 min of exercise in each bout. Heart rate and rating of perceived exertion (RPE) were determined at the same time intervals. The oxidation of CHO_total was 169.1 (12.9) g · 120 min⁻¹ and 203.1 (15.9) g · 120 min⁻¹ (P < 0.01) and that of FAT_total was 31.0 (4.2) g · 120 min⁻¹ and 17.1 (2.5) g · 120 min⁻¹ (P < 0.01) in CT and GT, respectively. GLU_exo oxidation in GT was 57.8 (4.3) g · 120 min⁻¹, or 34.2 (2.2)% of that ingested. Endogenous glucose oxidation was 169.1 (12.9) g · 120 min⁻¹ and 145.3 (11.9) g · 120 min⁻¹ (P < 0.01) in CT and GT, respectively. Insulin and glucose concentrations were higher in GT than in CT by 226% and 37%, respectively (both P < 0.05). Free fatty acids and glycerol concentrations were lower in GT than in CT, by 27% and 79%, respectively (both P < 0.05). Heart rate was similar between trials, but RPE was lower in GT vs CT at both 115 and 135 min. Thus, under these experimental conditions, GLU_exo intake spares endogenous carbohydrate and fat by 16% and 45%, respectively, contributes to approximately 25% of the total energy demand of exercise, and lowers the RPE. Accepted: 21 May 2000     

Elastic properties of muscle-tendon complex in long-distance runners

The purpose of this study was to investigate the elastic properties of muscle-tendon complex (MTC) in knee extensor muscles and the capacity for elastic energy utilization in long-distance runners (LDR) by comparing with data obtained from untrained individuals (CON). The elongation (L) of the tendon and aponeurosis of vastus lateralis muscle during isometric knee extension was determined by real-time brightness mode ultrasonography, while the subjects developed a gradually increasing torque from 0 (relaxed) to maximal effort (MVC) within 7 s. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The relationship between L muscle and force (F ) was curvilinear and consisted of an initial region (toe region), characterized by a large increase in L with increasing F, immediately followed by a linear region. The slope of the regression equation for the L-F relationship in the range 50%–100% of MVC was defined as an index of MTC compliance, where the rate of the changes in L to that in muscle F at every 10% of MVC became almost constant. The maximal L (L _max) and MTC compliance were significantly lower in LDR than in CON: 29.9 (SD 3.9) mm in LDR compared to 33.3 (SD 5.5) mm in CON for L _max and 1.55 (SD 0.25) × 10⁻² mm · N⁻¹ in LDR compared to 1.88 (SD 0.82) × 10⁻² mm · N⁻¹ in CON for MTC compliance. Also, LDR showed significantly less elastic energy absorption (E _e) than CON, defined as the area below the L-F relationship curve from 0 to 100% of MVC. Not only jump heights but also the differences between the heights in SJ and CMJ, expressed as the percentage of the height in SJ, were significantly lower in LDR than in CON. The augmentation with counter-movement was significantly correlated to either MTC compliance (r = 0.554, P < 0.05) or E _e (r = 0.563, P < 0.05). Thus, the present results would indicate that MTC of vastus lateralis muscle is less compliant and its potential for energy storage during MTS lengthening is lower in LDR than untrained individuals. These elastic profiles of vastus lateralis muscle in LDR may be associated with their lower performances during CMJ. Accepted: 3 September 1999     

Insecticidal Evaluation of essential oils of <Emphasis Type="BoldItalic">Citrus sinensis</Emphasis> L. (Myrtales: Myrtaceae) against housefly, <Emphasis Type="BoldItalic">Musca domestica</Emphasis> L. (Diptera: Muscidae)

The housefly, Musca domestica L., is one of the most common insects, associated with vectoring of various etiological agents. In order to search for effective control agent, the essential oil of sweet orange [Citrus sinensis (L.) Osbeck] was evaluated for its insecticidal activity against the larvae and pupae of housefly using contact toxicity and fumigation bioassays. In the contact toxicity assay, lethal concentration, LC₅₀ of C. sinensis essential oil against housefly larvae, varied between 3.93 and 0.71 μl/cm² for different observation days, while lethal time, LT₅₀, varied between 5.8 to 2.3 days. Mortality of larvae were significant with different concentrations (F = 2.79, df = 4, P < 0.05) and time (F = 6.69, df = 3, P < 0.01). In fumigant assay for housefly larvae, LC₅₀ of 71.2 and 52.6 μl/l was obtained in 24 and 48 h, respectively. Scanning electron microscopy of oil treated larvae revealed extreme dehydration and surface distortion while control larvae were free from any of the above symptoms and presented smooth surface, conforming effect of essential oil on housefly larvae. Percentage inhibition rate of oil against housefly pupae was 27.3–72.7% for contact toxicity and 46.4–100% for fumigation assay. Compositional analysis of C. sinensis essential oil using gas chromatography/mass spectrometry (GC-MS) revealed d-limonene (73.24%), α-pinene (5.86%) and myrcene (4.45%) as major components whereas its vapour profile (solid-phase micro extraction-GC/MS) was dominated by d-limonene at 92.57%. Significant activity of C. sinensis essential oil against larvae and pupae of housefly, pave the way for its use as eco-friendly housefly control measure.     

Infestation status of gnathiid isopod juveniles parasitic on Dusky grouper (<Emphasis Type="Italic">Epinephelus marginatus</Emphasis>) from the northeast Mediterranean Sea

This is the first detailed documented record of Gnathiid isopod praniza larvae infestating dusky grouper, (Epinephelus marginatus Lowe 1834) in the northeast Mediterranean Sea (36°36′N–36°07′E, 35°52′N–36°25′E). Fish were sampled monthly from Iskenderun Bay during a 3-year period from 2000 to 2003 [N = 468, W ± SD (range) = 503.69 ± 342.35 g (177–2,832 g), TL ± SD (range) = 32.39 ± 9.22 cm (16.1–67.0 cm), W _total = 0.213L _total ^2.19, r _total ² = 0.85]. Juveniles of the Gnathia sp. were only extracted from the epithelium of the buccal cavity. The monthly and seasonal patterns in infestation rates (mean prevalence, P = 27.35% and mean intensity, MI ± SD = 21.35 ± 16.19), and the relationship between length–weight and infested/non-infested fish were calculated. This study suggests that gnathiid parasite has no effect on the growth and general health condition of infested fish, although high intensities were observed in fish.     

Plasma catecholamine responses and neural adaptation during short-term resistance training

Low exercise-induced plasma adrenaline (A) responses have been reported in resistance-trained individuals. In the study reported here, we investigated the interaction between strength gain and neural adaptation of the muscles, and the plasma A response in eight healthy men during a short-term resistance-training period. The subjects performed 5 resistance exercises (E1–E5), consisting of 6 sets of 12 bilateral leg extensions performed at a 50% load, and with 2 days rest in between. Average electromyographic (EMG) signal amplitude was recorded before and after the exercises, from the knee extensor muscles in isometric maximal voluntary contraction (MVC) as well as during the exercises (aEMG_max and aEMG_exerc, respectively). Total oxygen consumed during the exercises (V˙O_2tot) was also measured. All of the exercises were exhaustive and caused significant decreases in MVC (34–36%, P < 0.001). As expected, the concentric one-repetition maximum (1-RM), MVC and aEMG_max were all higher before the last exercise (E5) than before the first exercise (E1; 7, 9 and 19%, respectively, P < 0.05). In addition, in E5 the aEMG_exerc:load and V˙O_2tot:load ratios were lower than in E1 (−5 and −14%, P < 0.05), indicating enhanced efficiency of the muscle contractions, However, the post-exercise plasma noradrenaline (NA) and A were not different in these two exercises [mean (SD) 10.2 (3.8) nmol · l⁻¹ vs 11.3 (6.0) nmol · l⁻¹, ns, and 1.2 (1.0) nmol · l⁻¹ vs 1.9 (1.1) nmol · l⁻¹, ns, respectively]. However, although NA increased similarly in every exercise (P < 0.01), the increase in A reached the level of statistical significance only in E1 (P < 0.05). The post-exercise A was also already lower in E2 [0.7 (0.7) nmol · l⁻¹, P < 0.05) than in E1, despite the higher post-exercise blood lactate concentration than in the other exercises [9.4 (1.1) mmol · l⁻¹, P < 0.05]. Thus, the results suggest that the observed attenuation in the A response can not be explained by reduced exercise-induced strain due to the strength gain and neural adaptation of the muscles. Correlation analysis actually revealed that those individuals who had the highest strength gain during the training period even tended to have an increased post-exercise A concentration in the last exercise as compared to first one (r=0.76, P < 0.05). Accepted: 10 February 2000     

Effects of drafting behind a two- or a six-beat kick swimmer in elite female triathletes

The metabolic and drag responses, together with the distance between the draftee and the leader, were studied in six female triathletes swimming behind a lead swimmer who used either a two- or a six-beat kick, at an average velocity of 1.24 m · s⁻¹ (range 1.20–1.31). Drag was measured by passive towing. Oxygen consumption [49.1 (3.8) versus 50.4 (5.0) ml · min⁻¹ · kg⁻¹], blood lactate [6.7 (2.3) versus 6.8 (1.9) mM], heart rate [172 (13.6) versus 173.5 (12.5) beats · min⁻¹), rating of perceived exertion [13.7 (1.2) versus 13.5 (1.0)], stroke rate [38.3 (1.5) versus 39.5 (1.4) cycle · min⁻¹], stroke length [1.95 (0.09) versus 1.89 (0.15) m · cycle⁻¹] were not statistically different between the two-beat and the six-beat kick situations. The energy cost of swimming per unit of distance [0.65 (0.06) versus 0.67 (0.08) ml O₂ · m⁻¹] and the passive drag were similar for both kicks. The distance separating the draftee from the lead swimmer was between 14 cm and 85 cm and was inversely correlated with passive drag: r=−0.82,P < 0.05, for the two-beat kick and r=−0.82, P <  0.05, for the six-beat kick. The higher the passive drag, the closer the hand of the draftee to the feet of the lead swimmer. It was of no more benefit to triathletes to draft behind a two-beat kick swimmer than behind a six-beat kick swimmer. Accepted: 10 April 2000     

Eosinophil Cationic Protein Stimulates TGF-β<Subscript>1</Subscript> Release by Human Lung Fibroblasts In Vitro

Eosinophilic inflammation and airway remodeling are features of asthma. Eosinophil cationic protein (ECP) is released by activated eosinophils and transforming growth factor (TGF)-β₁ has major functions in the fibrotic process. We therefore hypothesized that ECP stimulates TGF-β₁ release by human lung fibroblasts. Fibroblasts in monolayer displayed a constitutive release of TGF-β₁, which increased in presence of ECP (436 ± 60 vs. 365 ± 48 pg/ml at 48 h; P < 0.01). mRNA expression of TGF-β₁ was almost twofold in ECP-stimulated fibroblasts. ECP in three-dimensional cultures stimulated both TGF-β₁ release (180 ± 61 vs. 137 ± 54 pg/ml; P < 0.01) and fibroblast-mediated collagen gel contraction (28 vs. 39% of initial gel area at 48 h; P < 0.001). ECP stimulates TGF-β₁-release by human lung fibroblasts, suggesting a potential mechanism for eosinophils in the fibrotic response. This may be an important mechanism by which ECP promotes remodeling of extra cellular matrix leading to airway fibrosis in asthmatics.     

Relationship between muscle T2 * relaxation properties and metabolic state: a combined localized 31P-spectroscopy and 1H-imaging study

A multi-volume ³¹P-magnetic resonance spectroscopy localization procedure was implemented to compare directly muscle metabolism and proton T₂ ^* relaxation properties in the human plantar flexor muscles during exercise. Localized ³¹P-spectra were collected simultaneously from the medial gastrocnemius, lateral gastrocnemius and soleus muscles during exercise using β ₁-insensitive Hadamard Spectroscopic Imaging (HSI). ¹H T₂ ^*-weighted gradient-echo images were acquired at rest and immediately following high-intensity plantar flexion exercise. T₂ ^* mapping of the individual calf muscles showed that plantar flexion with the knee extended produces significant increases (P < 0.0001) in the mean (SEM) T₂ ^* of the medial [35.6 (1.2) ms vs 28.5 (0.5) ms at rest] and lateral gastrocnemius [35.6 (0.9) ms vs 26.2 (0.9) ms at rest], but not in the soleus [26.7 (0.6) ms vs 27.3 (0.8) ms at rest]. In accordance with the changes in T₂ ^*, the ratio of inorganic phosphate to phosphocreatine (P_i:PCr) and the intracellular muscle pH shifted significantly in the gastrocnemii, while the soleus showed no change in muscle pH and only a moderate increase in P_i-to-Ph. Comparison of spectroscopic and relaxation parameters in both gastrocnemius muscles revealed a significant relationship between post-exercise T₂ ^* and intracellular pH (r=0.72–0.76) and P_i-to-Ph ratios (r=0.81–0.88) during exercise. Using an improved method of localization, this study confirms the existence of a strong relationship between transverse relaxation properties and the metabolic state in skeletal muscles engaged in heavy exercise. Accepted: 28 December 1999     

Antimalarial drug interactions of compounds isolated from Kigelia africana (Bignoniaceae) and their synergism with artemether, against the multidrug-resistant W2mef Plasmodium falciparum strain

For decades, drug resistance has been the major obstacle in the fight against malaria, and the search for new drugs together with the combination therapy constitutes the major approach in responding to this situation. The present study aims at assessing the in vitro antimalarial activity of four compounds isolated from Kigelia africana stem bark (atranorin - KAE1, specicoside - KAE7, 2β,3β,19α-trihydroxy-urs-12-20-en-28-oic acid – KAE3, and p-hydroxy-cinnamic acid – KAE10) and their drug interactions among themselves and their combination effects with quinine and artemether. The antiplasmodial activity and drug interactions were evaluated against the multidrug-resistant W2mef strain of Plasmodium falciparum using the parasite lactate dehydrogenase assay. Three of the four compounds tested were significantly active against W2mef: specicoside (IC₅₀ = 1.02 ± 0.17 μM), 2β,3β,19α-trihydroxy-urs-12-en-28-oic acid (IC₅₀ = 1.86 ± 0.15 μM) and atranorin (IC₅₀ = 1.78 ± 0.18 μM), whereas p-hydroxy-cinnamic acid showed a weak activity (IC₅₀ = 12.89 ± 0.87 μM). A slight synergistic effect was observed between atranorin and 2β,3β,19α-trihydroxy-urs-12-en-28-oic acid (Combination index, CI = 0.82) whereas the interaction between specicoside and p-hydroxy-cinnamic acid were instead antagonistic (CI = 2.67). All the three compounds showed synergistic effects with artemether, unlike the slight antagonistic interactions of atranorin and 2β,3β,19α-trihydroxy-urs-12-en-28-oic acid in combination with quinine. K. africana compounds are therefore likely to serve as leads in the development of new partner drugs in artemether-based combination therapy.     

Cycling on Earth, in space, on the Moon

The mechanical power for cycling (P_c) at constant ground speed (s), in the absence of wind on smooth hard terrain is the sum of the power dissipated against rolling resistance, gravity and air resistance: P_c=a · s + M · g · s · sin γ + b · s ³, where a and b are constants, M is the mass of the subject plus bike, g is the acceleration of gravity and γ is the angle of the terrain with the horizontal. The constant b depends upon the drag coefficient (C_d), the overall area projected on the frontal plane (A _f), and the air density (ρ_a): b=0.5 · C_d · A _f · ρa. In turn, ρ_a depends on air pressure (P _B) and temperature (T): ρ_a=ρ₀ · 0.359 · P _B · T ⁻¹, where ρ₀ is the air density at 760 mmHg (101.3 kPa) and 273 K. The metabolic power developed by the cyclist (Ė _c) is related to P_c:Ė _c=P_c·η⁻¹, where η is the mechanical efficiency of cycling. The experimental values of a, b and η are fairly well known so that, if the maximal metabolic power as a function of the performance time is known for a given cyclist, the following set of data can be individually calculated: (1) best performances over any given distance and for any given altitude above sea level, (2) the effects of posture and body size on maximal speeds, and (3) the maximal incline of the terrain that can be overcome at any given speed or coasting speed for any given downslope. The above set of information makes it possible also to calculate the characteristics of a “Twin Bikes System” (TBS) for preventing microgravity deconditioning during long-term space flight. The TBS consists of two bicycles that are mechanically coupled by a differential gearing, which move at the very same speed, but in the opposite sense, along the inner wall of a cylindrically shaped space module. The circular trajectories induce a centrifugal acceleration vector (a _c) oriented along the head-to-feet direction of each subject: a _c=v _t ² · r ⁻¹ where v _t is the tangential velocity and r the radius of gyration, which is equal to the inner radius of the space module. So, any desired value of a _c can be achieved by appropriately selecting v _t, wherefrom the mechanical and metabolic powers that the astronauts must generate can be readily calculated. Experiments performed in a ground-based human centrifuge have shown that the discomfort derived from the rotating environment is reasonably low and well tolerated. If the appropriate atmospheric pressure is provided, cycling on circular or elliptical tracks may be useful to reduce cardiovascular deconditioning that occurs due to the reduced gravity in permanently manned lunar bases. Indeed, on the curved parts of the path a cyclist will generate a horizontal outward acceleration: a _c=s ² · r ⁻¹, where s is the velocity along the track and r is the radius of curvature. To counterbalance a _c, the subject plus bike must lean inwards so that the vectorial sum of a _c plus the lunar gravity (g _L=1.62 m · s⁻²) is applied along a straight line that includes the centre of mass of the system and the point of wheel contact with the ground. For values of s from 10 to 20 m · s⁻¹ and r from 50 to 200 m, this vectorial sum ranges from 1.05 to 5.03 g _L (0.17–0.83 g). Accepted: 20 March 2000     

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O_2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O_2max = 55.5 (4.4 SD) ml kg⁻¹ min⁻¹]. The RE was measured at 3 m s⁻¹ [65 (6)% V˙O_2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean = 17.4 ml min⁻¹). The V˙O₂ during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in V˙O₂ from RE1 to RE2 ranged from 3.4 to 4.7 ml kg⁻¹ min⁻¹ across treatments. In conclusion, the deterioration in RE at 3 m s⁻¹ (65% V˙O_2max) after 60 min of running at 80% V˙O_2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment. Accepted: 30 October 1997     

The effect of beta-blockade on plasma potassium concentrations and muscle excitability following static exercise

 The effects of β-blockade on plasma [K⁺], muscle excitability and force during fatiguing exercise were examined. Nine healthy males (mean age 22.3±1.7 yr) performed a 3-min fatigue protocol that consisted of a sustained submaximal contraction (30% of the maximal voluntary contraction, MVC) of the right quadriceps muscle. Subjects performed the exercise after treatment with either placebo, β₁-selective (metoprolol, 100 mg) or an equipotent dose of non-selective β_1,2-blockade (propranolol, 80 mg, n=6; 100 mg, n=2; 120 mg, n=1) twice daily for 3 days before testing according to a randomized double–blind design. Brachial arterial and femoral venous blood samples were drawn before, during, and for 15 min following the contraction, together with maximal stimulation of the right femoral nerve to evoke a twitch and a compound muscle action potential (M-wave); the M-wave amplitude being used as an index of sarcolemmal excitability. The exercise-induced rise in plasma [K⁺] did not differ between treatments, but K⁺ re-uptake during recovery was slower following propranolol. The recovery of the twitch was significantly related to the recovery of plasma [K⁺] in all trials, but the evoked M-waves were unaffected by either the contraction or the drug treatment. Propranolol resulted in a significantly (P<0.05) greater reduction (51.9±7.3%) in MVC following the 3-min contraction compared with metoprolol (40.7±3.6%) or placebo (38.9±3.6%). These results suggest that while β_1,2-blockade may significantly affect the recovery of muscle force and K⁺ homeostasis after fatiguing exercise (presumably through an inhibition of the Na⁺,K⁺-ATPase), it does not appear to affect surface membrane excitability. Received: 22 July 1997/Received after revision: 20 January 1998/Accepted: 23 January 1998     

Relationship between perceived exertion and mean power frequency of the EMG signal from the upper trapezius muscle during isometric shoulder elevation

The aim of the study was to investigate the relationship between a fatigue-induced increase of perceived exertion in the neck with a decrease of mean power frequency (MPF) in the surface electromyography (sEMG) signal during repeated shoulder elevation endurance tasks. About Thirty-two healthy women (age range 20–62) performed two maximum 6-min shoulder elevation endurance tasks at 30% of their maximal voluntary contraction (MVC) level, separated by a rest of 6 min. During these exercises, perceived exertion was estimated using the Borg scale (range 0–10), whereas the MPF of the sEMG signal from the upper trapezius was simultaneously detected. Linear regression analysis was applied over time for each trial and subject for both MPF and Borg scale rating values. The MPF was normalized by the intercept of the linear regression analysis. The resulting slopes of normalized mean power frequency (nMPF) and Borg scale rating were correlated with each other by linear regression for both trials. In order to investigate the individual behavior of fatigue effects between trials, Δ _{trial 2-trial 1} slopes of nMPF and Borg scale ratings were calculated for each subject. These slopes of nMPF and Borg scale ratings were correlated with each other as well by linear regression. The increase of Borg scale ratings, as well as the decrease of nMPF, were significantly higher in trial 2 than trial 1 (P<0.01). The results show a linear correlation between slopes of nMPF and Borg scale ratings for both trials 1 and 2 (r=0.76, P<0.01). Trial-to-trial slopes (Δ _{trial 2-trial 1}) of nMPF and Borg scale rating, were also significantly correlated (r=0.68, P<0.05). Thus, the individually sensed increase of perceived exertion in the neck during trial 2 was accompanied by a simultaneously higher detected decrease of nMPF. These findings indicate a close relationship between subjective perception of exertion in the neck and objectively assessed muscle fatigue of the upper trapezius.     

Continuous heart rate monitoring over 1 week in teenagers aged 11–16 years

Heart rate (HR) was monitored in 66 French pubertal boys (B, n=28) and girls (G, n=38) aged 11–16 years to evaluate habitual physical activity (HPA) over a 1-week period in the winter. The HR and the percentage of heart rate reserve (%HRR) were taken to be indexes of the metabolic activity for the whole day and for the different parts of the day. The HPA was evaluated from the time spent each day below 50%HRR, between 50%–70%HRR and above 70%HRR, which related to the time spent in no or low physical activity (NLPA), moderate physical activity (MPA) and vigorous physical activity (VPA), respectively. No sex differences were observed in the average %HRR each day {%HRR_mean, [B 30 (SD 4)%; G 32 (SD 4)%]} or in NLPA [B 715 (SD 61) min, G 711 (SD 81) min] and VPA [B 19 (SD 16) min, G 21 (SD 21) min] throughout the week. During school days, daily %HRR_mean was 7% smaller in 14–16 year olds compared to 11–13 year olds. This was linked to a decrease in MPA and a concomitant increase in NLPA (P<0.05). Daily %HRR_mean varied significantly during the week (range: 28–34% HRR). There were significant differences among the periods of the day (P<0.05). The HR was the greatest during physical education lessons [128 (SD 11) beats · min⁻¹], recreation [113 (SD 15) beats · min⁻¹] and lunch break [108 (SD 12) beats · min⁻¹] and the lowest during the evening [94 (SD 10) beats · min⁻¹]. It was only during the lunch breaks that %HRR_mean was greater (P<0.05) on school days than on free days. Of all the teenagers studied 32% were considered active during the week. Accepted: 9 June 1997     

Evaluation of the reliability and validity of a soccer-specific field test of repeated sprint ability

The reliability and validity of a soccer-specific field test of repeated sprint ability was assessed. Seven male games players performed the repeated sprint test on six separate occasions. The temporal pattern of the mean sprint time was analysed by using coefficient of variation with confidence intervals (CI), and repeated measures ANOVA. A within subject mean coefficient of variation of 1.8% (95% CI, 1.5–2.4) was found for performance in the repeated sprint test across all six trials. The mean coefficient of variation across trials 2–4 was found to be 1.9% (95% CI, 1.3–3.1), compared to trials 4–6, where it was 1.4% (95% CI, 1.0–2.3). The ANOVA showed that a significant difference was present between the trials (F _6,30 9.8, P < 0.001). A Tukey post-hoc test showed that significant differences were present between trial 1 and trials 3–6, and trial 2 and trial 5. The learning effect was complete by trial 3. Performance in the repeated sprint test was compared to total running time averaged from two repeats of the maximal anaerobic running test laboratory protocol. Mean sprint time in the repeated sprint test and total running time in the laboratory protocol had a correlation coefficient of r=−0.298 (P=0.516, n=7), suggesting that the energetics of the two tests are not closely related. In conclusion, this soccer-specific field test demonstrated high reliability. Accepted: 11 May 2000