Showing papers in "European Journal of Applied Physiology in 2008"

Identification of elderly fallers by muscle strength measures

Abstract: For efficient prevention of falls among older adults, individuals at a high risk of falling need to be identified. In this study, we searched for muscle strength measures that best identified those individuals who would fall after a gait perturbation and those who recovered their balance. Seventeen healthy older adults performed a range of muscle strength tests. We measured maximum and rate of development of ankle plantar flexion moment, knee extension moment and whole leg push-off force, as well as maximum jump height and hand grip strength. Subsequently, their capacity to regain balance after tripping over an obstacle was determined experimentally. Seven of the participants were classified as fallers based on the tripping outcome. Maximum isometric push-off force in a leg press apparatus was the best measure to identify the fallers, as cross-validation of a discriminant model with this variable resulted in the best classification (86% sensitivity and 90% specificity). Jump height and hand grip strength were strongly correlated to leg press force (r = 0.82 and 0.59, respectively) and can also be used to identify fallers, although with slightly lower specificity. These results indicate that whole leg extension strength is associated with the ability to prevent a fall after a gait perturbation and might be used to identify the elderly at risk of falling.

Validity of criteria for establishing maximal O2 uptake during ramp exercise tests.

Abstract: The incremental or ramp exercise test to the limit of tolerance has become a popular test for determination of maximal O(2) uptake (VO(2max)). However, many subjects do not evidence a definitive plateau of the VO(2) -work rate relationship on this test and secondary criteria based upon respiratory exchange ratio (RER), maximal heart rate (HR(max)) or blood [lactate] have been adopted to provide confidence in the measured VO(2max). We hypothesized that verification of VO(2max) using these variables is fundamentally flawed in that their use could either allow underestimation of VO(2max) (if, for any reason, a test were ended at a sub-maximal [Formula: see text]), or alternatively preclude subjects from recording a valid VO(2max). Eight healthy male subjects completed a ramp exercise test (at 20 W/min) to the limit of tolerance on an electrically braked cycle ergometer during which pulmonary gas exchange was measured breath-by-breath and blood [lactate] was determined every 90 s. Using the most widely used criterion values of RER (1.10 and 1.15), VO(2max) as determined during the ramp test (4.03 +/- 0.10 l/min) could be undermeasured by 27% (2.97 +/- 0.24 l/min) and 16% (3.41 +/- 0.15 l/min), respectively (both P or = 8 mM) were untenable because they resulted in rejection of 3/8 and 6/8 of the subjects, most of whom (5/8) had demonstrated a plateau of VO(2max) at VO(2max). These findings provide a clear mandate for rejecting these secondary criteria as a means of validating VO(2max) on ramp exercise tests.

Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones.

Abstract: Iron is utilised by the body for oxygen transport and energy production, and is therefore essential to athletic performance. Commonly, athletes are diagnosed as iron deficient, however, contrasting evidence exists as to the severity of deficiency and the effect on performance. Iron losses can result from a host of mechanisms during exercise such as hemolysis, hematuria, sweating and gastrointestinal bleeding. Additionally, recent research investigating the anemia of inflammation during states of chronic disease has allowed us to draw some comparisons between unhealthy populations and athletes. The acute-phase response is a well-recognised reaction to both exercise and disease. Elevated cytokine levels from such a response have been shown to increase the liver production of the hormone Hepcidin. Hepcidin up-regulation has a negative impact on the iron transport and absorption channels within the body, and may explain a potential new mechanism behind iron deficiency in athletes. This review will attempt to explore the current literature that exits in this new area of iron metabolism and exercise.

The contribution of upper limb and total body movement to adolescents' energy expenditure whilst playing Nintendo Wii.

Abstract: Little research documents the contribution of upper limb and total body movement to energy expenditure (EE) during active video gaming. To address this, EE, heart rate (HR), and, upper limb and total body movement were assessed in 11- to 17-year-old adolescents whilst playing three active (Nintendo Wii) and one sedentary (XBOX 360) video games. Non-dominant upper limb activity, EE and HR were significantly greater during Wii Sports boxing [mean 267.2 (SD 115.8) J kg−1 min−1; 136.7 (24.5) beats min−1] than tennis or bowling (P ≤ 0.044). For all active games hip activity best predicted EE (R 2 ≥ 0.53), with two-measure models of HR and single-site activity data, and multi-site activity data, similarly explaining the variance in EE (R 2 ≥ 0.64). The physiological cost of upper-body orientated active video games increased when movement of both upper limbs was encouraged. Improvements in EE explanatory power provide support for multi-site activity monitoring during unique, non-ambulatory activities.

Effect of hydrotherapy on the signs and symptoms of delayed onset muscle soreness.

Abstract: This study independently examined the effects of three hydrotherapy interventions on the physiological and functional symptoms of delayed onset muscle soreness (DOMS). Strength trained males (n = 38) completed two experimental trials separated by 8 months in a randomised crossover design; one trial involved passive recovery (PAS, control), the other a specific hydrotherapy protocol for 72 h post-exercise; either: (1) cold water immersion (CWI: n = 12), (2) hot water immersion (HWI: n = 11) or (3) contrast water therapy (CWT: n = 15). For each trial, subjects performed a DOMS-inducing leg press protocol followed by PAS or one of the hydrotherapy interventions for 14 min. Weighted squat jump, isometric squat, perceived pain, thigh girths and blood variables were measured prior to, immediately after, and at 24, 48 and 72 h post-exercise. Squat jump performance and isometric force recovery were significantly enhanced (P < 0.05) at 24, 48 and 72 h post-exercise following CWT and at 48 and 72 h post-exercise following CWI when compared to PAS. Isometric force recovery was also greater (P < 0.05) at 24, 48, and 72 h post-exercise following HWI when compared to PAS. Perceived pain improved (P < 0.01) following CWT at 24, 48 and 72 h post-exercise. Overall, CWI and CWT were found to be effective in reducing the physiological and functional deficits associated with DOMS, including improved recovery of isometric force and dynamic power and a reduction in localised oedema. While HWI was effective in the recovery of isometric force, it was ineffective for recovery of all other markers compared to PAS.

Reduced physical activity and risk of chronic disease: the biology behind the consequences.

Abstract: This review focuses on three preserved, ancient, biological mechanisms (physical activity, insulin sensitivity, and fat storage). Genes in humans and rodents were selected in an environment of high physical activity that favored an optimization of aerobic metabolic pathways to conserve energy for a potential, future food deficiency. Today machines and other technologies have replaced much of the physical activity that selected optimal gene expression for energy metabolism. Distressingly, the negative by-product of a lack of ancient physical activity levels in our modern civilization is an increased risk of chronic disease. We have been employing a rodent wheel-lock model to approximate the reduction in physical activity in humans from the level under which genes were selected to a lower level observed in modern daily functioning. Thus far, two major changes have been identified when rats undertaking daily, natural voluntary running on wheels experience an abrupt cessation of the running (wheel lock model). First, insulin sensitivity in the epitrochlearis muscle of rats falls to sedentary values after 2 days of the cessation of running, confirming the decline to sedentary values in whole-body insulin sensitivity when physically active humans stop high levels of daily exercise. Second, visceral fat increases within 1 week after rats cease daily running, confirming the plasticity of human visceral fat. This review focuses on the supporting data for the aforementioned two outcomes. Our primary goal is to better understand how a physically inactive lifestyle initiates maladaptations that cause chronic disease.

Do we really need a central governor to explain brain regulation of exercise performance

Abstract: In this paper two different models of brain regulation of exercise performance are critically compared: the central governor model proposed by Noakes and colleagues, and an alternative psycholobiological model based on motivational intensity theory.

The rate of increase in rating of perceived exertion predicts the duration of exercise to fatigue at a fixed power output in different environmental conditions

Abstract: This study tested the hypothesis that the increase in rating of perceived exertion (RPE) predicts the duration of exercise to exhaustion during exercise in hot conditions. Seven subjects performed five cycling trials in an environmental chamber at temperatures of 15°C (C) and 35°C (H). The cool trials were performed at intensities of 65 and 70% and the hot trials at 55, 60 and 65%. RPE, rectal and skin temperature were measured during trials. Duration to fatigue was significantly shorter in H65 and C70 than H60, C65 and H55 (P < 0.05). RPE rose linearly throughout each trial and the rate of increase in RPE was significantly faster in H65 and C70 than H55 (P < 0.05). There was an inverse linear relationship between trial duration and rate of increase in RPE (r = 0.83). Rectal temperature increased linearly throughout the trial and correlated significantly with RPE (r = 0.92). This study shows that the rate of increase in RPE predicts the duration of exercise to exhaustion at a constant power output in different environmental conditions.

Fatigue in repeated-sprint exercise is related to muscle power factors and reduced neuromuscular activity

Abstract: The purpose of this study was (1) to determine the relationship between each individual’s anaerobic power reserve (APR) [i.e., the difference between the maximum anaerobic (P ana) and aerobic power (P aer)] and fatigability during repeated-sprint exercise and (2) to examine the acute effects of repeated sprints on neuromuscular activity, as evidenced by changes in the surface electromyogram (EMG) signals. Eight healthy males carried out tests to determine P ana (defined as the highest power output attained during a 6-s cycling sprint), P aer (defined as the highest power output achieved during a progressive, discontinuous cycling test to failure) and a repeated cycling sprint test (10 × 6-s max sprints with 30 s rest). Peak power output (PPO) and mean power output (MPO) were calculated for each maximal 6-s cycling bout. Root mean square (RMS) was utilized to quantify EMG activity from the vastus lateralis (VL) muscle of the right leg. Over the ten sprints, PPO and MPO decreased by 24.6 and 28.3% from the maximal value (i.e., sprint 1), respectively. Fatigue index during repeated sprints was significantly correlated with APR (R = 0.87; P < 0.05). RMS values decreased over the ten sprints by 14.6% (±6.3%). There was a strong linear relationship (R 2 = 0.97; P < 0.05) between the changes in MPO and EMG RMS from the vastus lateralis muscle during the ten sprints. The individual advantage in fatigue-resistance when performing a repeated sprint task was related with a lower anaerobic power reserve. Additionally, a suboptimal net motor unit activity might also impair the ability to repeatedly generate maximum power outputs.

Role of muscle mass on sprint performance: gender differences?

Abstract: The aim of this study was to determine if gender differences in muscle mass explain the gender differences in running and cycling sprint performance. Body composition (dual-energy X-ray absorptiometry), and running (30 and 300 m test) and cycling (Wingate test) sprint performance were assessed in 123 men and 32 women. Peak power (PP) output in the Wingate test expressed per kg of lower extremities lean mass (LM) was similar in males and females (50.4 +/- 5.6 and 50.5 +/- 6.2 W kg(-1), P = 0.88). No gender differences were observed in the slope of the linear relation between LM and PP or mean power output (MP). However, when MP was expressed per kg of LM, the males attained a 22% higher value (26.6 +/- 3.4 and 21.9 +/- 3.2 W kg(-1), P < 0.001). The 30 and 300-m running time divided by the relative lean mass of the lower extremities (RLM = LM x 100/body mass) was significantly lower in males than in females. Although, the slope of the linear relationship between RLM and 300-m running time was not significantly different between genders, the males achieved better performance in the 300-m test than the females. The main factor accounting for gender differences in peak and mean power output during cycling is the muscle mass of the lower extremities. Although, the peak power generating capability of the muscle is similar in males and females, muscle mass only partially explains the gender difference in running sprints, even when expressed as a percentage of the whole body mass.

Recovery after an Ironman triathlon: sustained inflammatory responses and muscular stress

Abstract: Ultra-endurance exercise, such as an Ironman triathlon, induces muscle damage and a systemic inflammatory response. As the resolution of recovery in these parameters is poorly documented, we investigated indices of muscle damage and systemic inflammation in response to an Ironman triathlon and monitored these parameters 19 days into recovery. Blood was sampled from 42 well-trained male triathletes 2 days before, immediately after, and 1, 5 and 19 days after an Ironman triathlon. Blood samples were analyzed for hematological profile, and plasma values of myeloperoxidase (MPO), polymorphonuclear (PMN) elastase, cortisol, testosterone, creatine kinase (CK) activity, myoglobin, interleukin (IL)-6, IL-10 and high-sensitive C-reactive protein (hs-CRP). Immediately post-race there were significant (P < 0.001) increases in total leukocyte counts, MPO, PMN elastase, cortisol, CK activity, myoglobin, IL-6, IL-10 and hs-CRP, while testosterone significantly (P < 0.001) decreased compared to prerace. With the exception of cortisol, which decreased below prerace values (P < 0.001), these alterations persisted 1 day post-race (P < 0.001; P < 0.01 for IL-10). Five days post-race CK activity, myoglobin, IL-6 and hs-CRP had decreased, but were still significantly (P < 0.001) elevated. Nineteen days post-race most parameters had returned to prerace values, except for MPO and PMN elastase, which had both significantly (P < 0.001) decreased below prerace concentrations, and myoglobin and hs-CRP, which were slightly, but significantly higher than prerace. Furthermore, significant relationships between leukocyte dynamics, cortisol, markers of muscle damage, cytokines and hs-CRP after the Ironman triathlon were noted. This study indicates that the pronounced initial systemic inflammatory response induced by an Ironman triathlon declines rapidly. However, a low-grade systemic inflammation persisted until at least 5 days post-race, possibly reflecting incomplete muscle recovery.

Effect of 5 weeks horizontal bed rest on human muscle thickness and architecture of weight bearing and non-weight bearing muscles

Abstract: The aim of the present study was to investigate the changes in thickness, fascicle length (L f) and pennation angle (θ) of the antigravity gastrocnemius medialis (GM) and vastus lateralis (VL) muscles, and the non-antigravity tibialis anterior (TA) and biceps brachii (BB) muscles measured by ultrasonography in ten healthy males (aged 22.3 ± 2.2 years) in response to 5 weeks of horizontal bed rest (BR). After BR, muscle thickness decreased by 12.2 ± 8.8% (P < 0.05) and 8.0 ± 9.1% (P < 0.005) in the GM and VL, respectively. No changes were observed in the TA and BB muscles. L f and θ decreased by 4.8 ± 5.0% (P < 0.05) and 14.3 ± 6.8% (P < 0.005) in the GM and by 5.9 ± 5.3% (P < 0.05) and 13.5 ± 16.2% (P < 0.005) in the VL, again without any changes in the TA and BB muscles. The finding that amongst the antigravity muscles of the lower limbs, the GM deteriorated to a greater extent than the VL is possibly related to the differences in relative load that this muscle normally experiences during daily loading. The dissimilar response in antigravity and non-antigravity muscles to unloading likely reflects differences in loading under normal conditions. The significant structural alterations of the GM and VL muscles highlight the rapid remodelling of muscle architecture occurring with disuse.

Association of the ACTN3 R577X polymorphism with power athlete status in Russians.

Abstract: The alpha-actinin-3 (ACTN3) gene encodes a Z-disc structural protein which is found only in fast glycolytic muscle fibers. A common nonsense polymorphism in codon 577 of the ACTN3 gene (R577X) results in alpha-actinin-3 deficiency in XX homozygotes. Previous reports have shown a lower proportion of the ACTN3 XX genotype in power-oriented athletes compared to the general population. In the present study we tested whether XX genotype was under-represented in Russian power-oriented athletes. The study involved 486 Russian power-oriented athletes of regional or national competitive standard. ACTN3 genotype and allele frequencies were compared to 1,197 controls. The frequencies of the ACTN3 XX genotype (6.4 vs. 14.2%; P < 0.0001) and X allele (33.3 vs. 38.7%; P = 0.004) were significantly lower in power-oriented athletes compared to controls. Furthermore, the lowest (3.4%) frequency of the ACTN3 XX genotype was found in a group of highly elite athletes, supporting the hypothesis that the presence of alpha-actinin-3 has a beneficial effect on the function of skeletal muscle in generating forceful contractions at high velocity. In conclusion, ACTN3 R577X polymorphism was associated with power athlete status in Russians.

Heart rate variability at different thermal comfort levels

Abstract: The mechanism of human thermal comfort is important for building a comfortable and healthy indoor environment. This paper analyzes human heart rate variability (HRV) at different thermal comfort levels and discusses the mechanism of human thermal comfort. A total of 33 subjects were divided in 3 groups. Under air temperatures of 21, 24, 26, 28, 29, and 30 degrees C, the subjects' electrocardiogram was recorded for 5 min. HRV (the ratio of absolute powers in low- and high-frequency bands, LF/HF ratio) was analyzed. LF/HF at discomfort level were significantly higher than that at comfort level (P < 0.05), despite the same thermal sensation. The results indicate that sympathetic activity plays an important role in subjects' thermal discomfort and the LF/HF ratio may be used as an indicator for human thermal comfort.

Whole muscle contractile parameters and thickness loss during 35-day bed rest

Abstract: Extended exposure to microgravity leads to significant musculoskeletal adaptations. Contractile parameters of four skeletal muscles (biceps brachii–BB, vastus medialis–VM, biceps femoris–BF and gastrocnemius medialis–GM) were measured in ten healthy males (aged 22.3 ± 2.2 years) during 35 days of horizontal bed rest by a mechanomyography-based method termed ‘tensiomyography’ (TMG). Two contractile parameters: contraction time (Tc) and maximal displacement (Dm) were individually measured from electrically evoked maximal single twitch TMG response of all four muscles before and after bed rest. Significant changes in Tc were found after bed rest, as shown by an increase in GM muscle Tc by 18% (p < 0.01). Dm values significantly increased (p < 0.01) after bed rest, by 24, 26 and 30% in the VM, BF and GM muscles, respectively. In the GM, the change in Dm significantly correlated with the decrease in muscle thickness (r = −0.70, p < 0.01). In conclusion, bed rest induced changes in both Dm and Tc of the TMG signal; changes in Dm being inversely related to those of muscle thickness. Amongst the investigated muscles, most affected, in terms of atrophy and mechanical alterations, were those of the lower limbs. The observed increase in Dm may be attributed to a decrease in muscle, as well as tendon stiffness, causing larger muscle fibre and non-contractile tissue oscillations following contraction.

Investigation of gender difference in thermal comfort for Chinese people

Abstract: Gender difference in thermal comfort for Chinese people was investigated through two laboratory experiments. Both subjective assessment and objective measurement were taken during the experiment. Skin temperature (17 points) and heart rate variability (HRV) were measured in one of the experiment. Our results show that there are gender differences in thermal comfort for Chinese people. Correlation of thermal sensation votes and air temperature and vapor pressure shows that females are more sensitive to temperature and less sensitive to humidity than males. Subjective assessment, skin temperature and HRV analysis suggest that females prefer neutral or slightly warmer condition, due to their constantly lower skin temperature and the fact that mean skin temperature is a good predictor of sensation and discomfort below neutrality. Female comfortable operative temperature (26.3°C) is higher than male comfortable operative temperature (25.3°C), although males and females have almost the same neutral temperature and that there is no gender difference in thermal sensation near neutral conditions.

The rate of muscle temperature increase during acute whole-body vibration exercise

Abstract: This study compared the rate of muscle temperature (T m) increase during acute whole-body vibration (WBV), to that of stationary cycling and passive warm-up. Additionally we wanted to determine if the purported increase in counter-movement jump and peak power cycling from acute WBV could be explained by changes in muscle temperature. Eight active participants volunteered for the study, which involved a rest period of 30 min to collect baseline measures of muscle, core, skin temperature, heart rate (HR), and thermal leg sensation (TLS), which was followed by three vertical jumps and 5 s maximal cycle performance test. A second rest period of 40 min was enforced followed by the intervention and performance tests. The change in T m elicited during cycling was matched in the hot bath and WBV interventions. Therefore cycling was performed first, proceeded by, in a random order of hot bath and acute WBV. The rate of T m was significantly greater (P < 0.001) during acute WBV (0.30°C min−1) compared to cycle (0.15°C min−1) and hot bath (0.09°C min−1) however there was no difference between the cycle and hot bath, and the metabolic rate was the same in cycling and WBV (19 mL kg−1 min−1). All three interventions showed a significant (P < 0.001) increase in countermovement jump peak power and height. For the 5 s maximal cycle test (MIC) there were no significant differences in peak power between the three interventions. In conclusion, acute WBV elevates T m more quickly than traditional forms of cycling and passive warm-up. Given that all three warm-up methods yielded the same increase in peak power output, we propose that the main effect is caused by the increase in T m.

Male and female upper body sweat distribution during running measured with technical absorbents

Abstract: Body sweat distribution over the upper body in nine clothed male and female runners of equal fitness while running at 65% \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2max}}}} \) and subsequent 15-min rest in a moderate climate (25°C, 53% rh) was investigated using technical absorbent materials to collect the sweat produced. No significant difference in whole body mass loss (male 474 SD 80; female 420 SD 114 g m−2 h−1) nor surface weighted average of all tested zones for exercise (male 636 SD 165; female 565 SD 222 g m−2 h−1) nor rest (male 159 SD 46; female 212 SD 75 g m−2 h−1) were observed. Local sweat rate (LSR) ranges were large and overlapped substantially in most areas. Males showed higher LSR for the mid-front (P < 0.05), sides (P < 0.05), and mid lateral back (P < 0.01) compare to females. Both sexes showed similar sweat distribution patterns over the upper body with some exceptions. Males showed higher relative (local to overall) sweat rates than females for the mid lateral back (P < 0.001), while it was lower for the upper arm (P < 0.001), lateral lower back (P < 0.05), and upper central back (P < 0.05). Sweating in both sexes was highest along the spine, and higher on the back as a whole than the chest as a whole. Upper arm sweat rate was lowest. Males showed a higher ratio of highest to lowest LSR (4.4 vs. 2.8; P < 0.05). The present study has provided more detailed information, based on more subjects, on upper body sweat distribution than previously available, which can be used in clothing design, thermo-physiological modelling, and thermal manikin design.

Effect of hydrotherapy on the signs and symptoms of delayed onset muscle soreness (vol 103, 2008)

Abstract: The purpose of this study was to examine the effects of three hydrotherapy interventions on the physiological and functional symptoms of delayed onset muscle soreness (DOMS). A total of 38 strength trained males completed two experimental trials separated by eight months in a randomised crossover design; one trial involved passive recovery (PAS, control), the other a specific hydrotherapy protocol. Subjects were randomly assigned to one of three groups differing only in recovery intervention: 1) cold water immersion (CWI, 15◦C), 2) hot water immersion (HWI, 38◦C) or 3) contrast water therapy (CWT, 15◦C/38◦C). For each trial subjects performed a DOMS-inducing leg press protocol consisting of 5x10 eccentric contractions at 120% one repetition max (1RM), followed by 2x10 eccentric contractions at 1RM, with three minutes rest between sets. Weighted squat jump, isometric squat, perceived pain, thigh girths and blood variables were measured prior to, immediately after, then 24, 48 and 72 hours post-exercise. Following testing on each day subjects completed one of the recovery interventions (CWI, HWI, CWT or PAS) for 14 minutes. Recovery of squat jump performance was significantly enhanced (P<0.05) at 24, 48 and 72 hours post exercise following CWT (mean difference from baseline expressed as a percentage; -6.2, -3.1, 0.3%) when compared to PAS (-14.5, -12.3, -7.5%) and at 48 and 72 hours post-exercise following CWI (-5.8, -1.9%) when compared to PAS (-15.9, -7.3%). Additionally, recovery of isometric force was significantly greater at 24, 48, and 72 hours post-exercise following CWT (-10.3, -7.4, -2.8%) and HWI (-12.8, -10.1, -3.2%) and also significantly improved at 48 and 72 hours post-exercise following CWI (-7.3, -4.3) compared to PAS. Significant decreases in mid thigh girth were observed at 24, 48, and 72 hours post-exercise following both CWI (0.7, 0.4, 0.3%) and CWT (0.5, 0.2, 0.1%) compared to girth measurements following PAS (≈ 0.81.5%) and HWI (≈ 0.5-1.3%). Perceived pain was only improved (P<0.01) following CWT at 24, 48 and 72 hours post-exercise. The only significant reduction (P<0.05) in any of the blood markers monitored was observed in Creatine Kinase concentration at 24 and 72 hours post-exercise following CWI. Both CWT and CWI were associated with a smaller reduction and faster restoration of isometric force and squat jump performance. While HWI improved isometric force production, no beneficial effects were observed in squat jump performance over time. Compared to PAS and HWI, CWT and CWI appeared to reduce localised oedema that has been associated with DOMS. In conclusion, CWT and CWI recovery interventions appear able to reduce, and improve recovery from, the physiological and function symptoms associated with DOMS.

The effect of the Ramadan fast on physical performance and dietary habits in adolescent soccer players.

Abstract: The purpose of this study was to examine the effect of the Ramadan fast on performance capacities, dietary habits, and the daily behavioral patterns in adolescent (14–16-year-old) soccer players. Nineteen male players performed a series of fitness tests before and at the end of Ramadan fast. Caloric intake, physical activity pattern and sleep habits were evaluated during the week before the Ramadan fast and during the last week of the Ramadan fast. The fast resulted in a significant reduction in aerobic capacity [3,000 m run time (mean ± SD): 812.8 ± 73.3 s vs. 819.9 ± 73.4 s, P < 0.001], speed endurance (Sum 6 × 40 m run time: 46.36 ± 1.36 s vs. 46.73 ± 1.31 s, P < 0.001, and performance decrement: 9.0 ± 1.5% vs. 9.5 ± 1.7%, P < 0.05), and jumping performance (44.8 ± 4.5 cm vs. 44.0 ± 4.5 cm, P < 0.05), but had no significant effect on sprint performance (7.38 ± 0.25 s vs. 7.40 ± 0.26 s, P = 0.20) or agility (4 × 10 m shuttle run time: 9.53 ± 0.35 s vs. 9.55 ± 0.37 s, P = 0.26). Daily intense physical activity was significantly reduced during Ramadan (6.4 ± 0.2 h/week vs. 4.5 ± 0.1 h/week, P < 0.005). There were no significant differences in total caloric intake (3012 ± 412 kcal/day vs. 3240 ± 348 kcal/day, P = 0.39) or total daily sleeping hours (8.6 ± 0.7 h/day vs. 8.6 ± 0.5 h/day, P = 0.80) between Ramadan and a regular month. The results indicate that Ramadan fasting can lead to a significant decrease in athletic performance capacities. The decrease in performance does not necessarily relate to changes in caloric intake and sleeping hours during the fast.

Effect of speed on the energy cost of walking in unilateral traumatic lower limb amputees

Abstract: In this work, the effect of walking speed on the energy expenditure in traumatic lower-limb amputees was studied. The oxygen consumption was measured in 10 transfemoral amputees, 9 transtibial amputees and 13 control subjects, while they stood and walked at different speeds from 0.3 m s−1 to near their maximum sustainable speed. Standing energy expenditure rate was the same in lower-limb amputees and in control subjects (≈1.85 W kg−1). On the contrary, during walking, the net energy expenditure rate was 30–60% greater in transfemoral amputees and 0–15% greater in transtibial amputees than in control subjects. The maximal sustainable speed was about 1.2 m s−1 in transfemoral amputees and 1.6 m s−1 in transtibial amputees, whereas it was above 2 m s−1 in control subjects. Among these three groups, the cost of transport versus speed presented a U-shaped curve; the minimum cost increased with the level of amputation, and the speed at which this minimum occurred decreased.

Cortical activity of skilled performance in a complex sports related motor task.

Abstract: A skilled player in goal-directed sports performance has the ability to process internal and external information in an effective manner and decide which pieces of information are important and which are irrelevant. Focused attention and somatosensory information processing play a crucial role in this process. Electroencephalographic (EEG) recordings are able to demonstrate cortical changes in conjunction with this concept and were examined during a golf putting performance in an expert-novice paradigm. The success in putting (score) and performance-related cortical activity were recorded with an EEG during a 5 x 4 min putting series. Subjects were asked to putt balls for four min at their own pace. The EEG data was divided into different frequencies: Theta (4.75-6.75 Hz), Alpha-1 (7-9.5 Hz), Alpha-2 (9.75-12.5 Hz) and Beta-1 (12.75-18.5 Hz) and performance related power values were calculated. Statistical analysis shows significant better performance in the expert golfers (P < 0.001). This was associated with higher fronto-midline Theta power (P < 0.05) and higher parietal Alpha-2 power values (P < 0.05) compared to the novices in golf putting. Frontal Theta and parietal Alpha-2 spectral power in the ongoing EEG demonstrate differences due to skill level. Furthermore the findings suggest that with increasing skill level, golfers have developed task solving strategies including focussed attention and an economy in parietal sensory information processing which lead to more successful performance. In a theoretical framework both cortical parameters may play a role in the concept of the working memory.

Levels of agreement for RR intervals and short-term heart rate variability obtained from the Polar S810 and an alternative system

Abstract: The aim of this study was to assess the agreement between HRV measures derived from a time series of RR intervals recorded by a standard 12-lead ECG (CP) and a commercially available RR interval recorder (S810). Thirty-three participants (19 males) (median age 36, range 20-63) underwent simultaneous, 5-min, supine RR-interval recordings. Each RR interval time series was analysed using the software supplied with the recording equipment. Two comparisons were then made. First, a comparison of RR interval data recording and editing only was made. Second, comparisons were made for measures of HRV derived from edited RR interval data. Agreement between RR intervals and standard HRV measures were assessed using intraclass correlation coefficient and limits of agreement. Agreement of HRV measures derived from RR intervals recorded and edited by individual systems was not acceptable. Agreement analyses for the number of RR intervals recorded and edited by each systems software showed excellent intraclass correlation coefficients (ICC lower 95% CI > 0.75) and acceptably narrow limits of agreement (LoA). These data indicate that the number of RR intervals recorded by S810 can agree well those recorded from a standard 12-lead ECG. This is true even after application of system specific data editing procedures. Commercial RR-interval recorders may offer a simple, inexpensive alternative to full 12-lead ECG in the recording and editing of RR intervals for subsequent HRV analysis in healthy populations.

The influence of stroke mechanics into energy cost of elite swimmers

Abstract: The purpose of this study was to analyze the relationships between energy cost (C), swimming velocity (v), stroke frequency (SF) and stroke length (SL) in top-level swimmers. Eighteen elite swimmers (four freestylers, five backstrokers, five breaststrokers and four butterflyers) performed an intermittent set of n × 200 m swims (n ≤ 8) with increasing velocity. The oxygen consumption was measured breath-by-breath by a portable metabolic cart (K4 b2, Cosmed, Rome, Italy). A respiratory snorkel and valve system with low hydrodynamic resistance was used to measure pulmonary ventilation and collect expiratory gases. Blood samples were taken from the ear lobe before and after each swim to analyze the blood lactate concentration (YSI 1500L, Yellow Springs, OH, USA). At Backstroke, Breaststroke and Butterfly strokes, increases of SF were associated to increases of C, even when controlling the v. The increases in SL only promoted significant decreases in the C in Breaststroke. There was a significant and polynomial relationship between v and SF for all competitive swimming techniques. The polynomial relationship between v and SL was significant only in Freestyle and Butterfly stroke. Partial correlations between v and SF controlling the effect of SL and between v and SL controlling the effect of SF, were positive and significant for all techniques. It is concluded that manipulation of stroke mechanics variables (SF and SL) may be one of the factors through which C in competitive swimming can be altered for a given v.

Decrease in Akt/PKB signalling in human skeletal muscle by resistance exercise

Abstract: We analysed the effects of resistance exercise upon the phosphorylation state of proteins associated with adaptive processes from the Akt/PKB (protein kinase B) and the mitogen-activated protein kinase (MAPK) pathways. Nine healthy young men (21.7 +/- 0.55 year) performed 10 sets of 10 leg extensions at 80% of their 1-RM (repetition maximum). Muscle biopsies were taken from the vastus lateralis at rest, within the first 30 s after exercise and at 24 h post-exercise. Immediately post exercise, the phosphorylation states of Akt/PKB on Thr308 and Ser473 and 4E-BP1 on Thr37/46 (eukaryotic initiation factor 4E-binding protein 1) were decreased (-60 to -90%, P < 0.05). Conversely, the phosphorylation of p70(s6k) (p70 ribosomal S6 kinase) on Thr421/Ser424 was increased more than 20-fold (P < 0.05), and this was associated with a 10- to 50-fold increase in the phosphorylation of p38 and ERK1/2 (extracellular signal-regulated kinase) (P < 0.05). Twenty-four hours post-exercise the phosphorylation state of Akt/PKB on Thr308 was depressed, whereas the phosphorylation of p70(s6k) on Thr421/Ser424 and sarcoplasmic ERK1/2 were elevated. The present results indicate that high-intensity resistance exercise in the fasted state inhibits Akt/PKB and 4E-BP1 whilst concomitantly augmenting MAPK signalling and p70(s6k) on Thr421/Ser424.

Mechanical stimuli of skeletal muscle: implications on mTOR/p70s6k and protein synthesis

Abstract: The skeletal muscle is a tissue with adaptive properties which are essential to the survival of many species. When mechanically stimulated it is liable to undergo remodeling, namely, changes in its mass/volume resulting mainly from myofibrillar protein accumulation. The mTOR pathway (mammalian target of rapamycin) via its effector p70s6k (ribosomal protein kinase S6) has been reported to be of importance to the control of skeletal muscle mass, particularly under mechanical stimulation. However, not all mechanical stimuli are capable of activating this pathway, and among those who are, there are differences in the activation magnitude. Likewise, not all skeletal muscle fibers respond to the same extent to mechanical stimulation. Such evidences suggest specific mechanical stimuli through appropriate cellular signaling to be responsible for the final physiological response, namely, the accumulation of myofibrillar protein. Lately, after the mTOR signaling pathway has been acknowledged as of importance for remodeling, the interest for the mechanical/chemical mediators capable of activating it has increased. Apart from the already known MGF (mechano growth factor), some other mediators such as phosphatidic acid (PA) have been identified. This review article comprises and discusses relevant information on the mechano-chemical transduction of the pathway mTOR, with especial emphasis on the muscle protein synthesis.

Efficacy of body ventilation system for reducing strain in warm and hot climates.

Abstract: This study determined whether a torso-vest forced ambient air body ventilation system (BVS) reduced physiological strain during exercise-heat stress. Seven heat-acclimated volunteers attempted nine, 2-h treadmill walks at 200 W m−2 in three environments, −40°C, 20% rh (HD), 35°C, 75% rh (HW), and 30°C, 50% rh, (WW) wearing the Army Combat Uniform, interceptor body armor (IBA) and Kevlar helmet. Three trials in each environment were BVS turned on (BVSOn), BVS turned off (BVSOff), and no BVS (IBA). In HD, BVSOn significantly lowered core temperature (T re), heart rate (HR), mean skin temperature (T sk), mean torso skin temperature (T torso), thermal sensation (TS), heat storage (S), and physiological strain index (PSI), versus BVSOff and IBA (P < 0.05). For HW (n = 6), analyses were possible only through 60 min. Exercise tolerance time (min) during HW was significantly longer for BVSOn (116 ± 10 min) versus BVSOff (95 ± 22 min) and IBA (96 ± 18 min) (P < 0.05). During HW, BVSOn lowered HR at 60 min versus IBA, T sk from 30 to 60 min versus BVSOff and IBA, and PSI from 45 to 60 min versus BVSOff and at 60 min versus IBA (P < 0.05). BVSOn changes in T re and HR were lower in HD and HW. During WW, BVSOn significantly lowered HR, T sk, and T torso versus BVSOff and IBA (P < 0.05) during late exercise. Sweating rates were significantly lower for BVSOn versus BVSOff and IBA in both HD and WW (P < 0.05), but not HW. These results indicate that BVSOn reduces physiological strain in all three environments by a similar amount; however, in hot-dry conditions the BVSOff increases physiological strain.

The energetic and cardiovascular response to treadmill walking and cycle ergometer exercise in obese women

Abstract: Physical activity is essential in obesity management, but exercise capacity is compromised in obese individuals due to the excessive body mass, impacting on body movement's energetics, and to the dysfunctions of regulatory mechanisms, affecting cardiovascular responses. This study aims to compare the energetics and cardiovascular responses of walking and cycling in obese women, and to formulate recommendations regarding the most suitable type of exercise for obesity. Fifteen obese (OB) and six normal weight (NW) women exercised on treadmill (TM) and cycle ergometer (CE). During both exercise modalities, metabolic rate was higher in OB than in NW and correlated with measures of body mass. Leg movement metabolic rate during cycling depended upon individual adiposity, and when accounted for, mechanical efficiency was similar in the two groups. When accounting for extra mass, differences in metabolic rate among groups are abolished for CE, indicating no obesity impairment of muscle efficiency, but not for TM, suggesting that differences in biomechanics may explain the higher net cost of transport of OB. In both groups, HR was higher during CE than TM at the same oxygen uptake (VO(2)), but in OB the HR increment over VO(2) was greater for CE than for TM. Therefore, due to different cardiovascular responses to TM and CE in OB, walking is more convenient, enabling OB to attain target energy expenditure at lower HR or in a shorter time.

Skeletal muscle properties and fatigue resistance in relation to smoking history

Abstract: Although smoking-related diseases, such as chronic obstructive pulmonary disease (COPD), are often accompanied by increased peripheral muscle fatigability, the extent to which this is a feature of the disease or a direct effect of smoking per se is not known. Skeletal muscle function was investigated in terms of maximal voluntary isometric torque, activation, contractile properties and fatigability, using electrically evoked contractions of the quadriceps muscle of 40 smokers [19 men and 21 women; mean (SD) cigarette pack years: 9.9 (10.7)] and age- and physical activity level matched non-smokers (22 men and 23 women). Maximal strength and isometric contractile speed did not differ significantly between smokers and non-smokers. Muscle fatigue (measured as torque decline during a series of repetitive contractions) was greater in smokers (P = 0.014), but did not correlate with cigarette pack years (r = 0.094, P = 0.615), cigarettes smoked per day (r = 10.092, P = 0.628), respiratory function (%FEV(1pred)) (r = -0.187, P = 0.416), or physical activity level (r = -0.029, P = 0.877). While muscle mass and contractile properties are similar in smokers and non-smokers, smokers do suffer from greater peripheral muscle fatigue. The observation that the cigarette smoking history did not correlate with fatigability suggests that the effect is either acute and/or reaches a ceiling, rather than being cumulative. An acute and reversible effect of smoking could be caused by carbon monoxide and/or other substances in smoke hampering oxygen delivery and mitochondrial function.

Physiological and subjective responses to cooling devices on firefighting protective clothing

Abstract: The aim of the present study was to examine the effectiveness of ice-packs (ICE) and phase change material (PCM) cooling devices in reducing physiological load based on subjects’ physiological and subjective responses while the subjects exercised on a bicycle ergometer while wearing firefighting protective clothing in a relatively high temperature environment (30°C, 50%RH). Subjects were eight graduate students, aged 25.9 years (SD 3.2). Each subject participated in four 50-min exposures: control (CON), ICE, PCM of 5°C [PCM(5)] and 20°C [PCM(20)]. Each subject rested in a pre-test room for 10 min before entering the test-room where they rested for another 10 min, followed by 30 min-exercise and a 10 min-recovery period. The exercise intensity was set at 55%VO2max. Cooling effects were evaluated by measuring rectal temperature (Tre), mean skin temperature (Tsk), body weight loss and subjective responses. An increase in Tre for PCM(5) and PCM(20) which was less than that for CON and ICE was observed. The increases in Tsk were depressed using cooling devices, but the cooling effects of PCMs were greater than ICE. The subjects with CON felt hotter and wetter than those in the other conditions. The larger surface cooling area, higher melting temperature and softer material of PCMs which reduces absorption capacity caused a decrease in Tre and Tsk for PCM(5) and PCM(20) which was more than that for CON and ICE. Furthermore, PCM(20) does not require refrigeration. These results suggest that PCM(20) is more effective than other cooling devices in reducing the physiological load while wearing firefighting protective clothing.