Plasma K+ changes during intense exercise in endurance-trained and sprint-trained subjects

Active muscle releases K⁺, and the plasma K⁺ concentration is consequently raised during exercise. K⁺ is removed by the NaK pump, and training may influence the number of pumps. The plasma K⁺ concentration was therefore studied in five endurance-trained (ET) and six sprint-trained (ST) subjects during and after 1 min of exhausting treadmill running. Non-exhausting bouts of exercise at either lower speed or of shorter duration were also carried out. Blood samples were taken from a catheter in the femoral vein before and at frequent intervals after exercise. The pre-exercise venous plasma [K⁺] was (mean ± SEM) 3.68±0.10mmol l^-1 (ET) and 3.88 ± 0.06 mmol l^-1 (ST). One minute of exhausting exercise was sustained at 5.27 ±0.08 m s^-1 (ET) and 5.59 ± 0.06 m s^-1 (ST) and caused the plasma K⁺ concentration to rise by 4.4 ± 0.3 (ET) and 4.7 ± 0.3 mmol l^-1 (ST; ns) respectively. Three minutes after exercise the K⁺ concentration was 0.48 + 0.08 mmol l^-1 (ST) and 0.50 ± 0.07 mmol l^-1 (ST) below the pre-exercise value. During the following 6 min of recovery, the value was unchanged for the ET subjects, while a 0.32 ± 0.06 mmol l^-1 rise was seen for the ST subjects. Exercise at reduced intensity or of reduced duration resulted in smaller changes in the K⁺ concentration both during exercise and in the post-exercise recovery, and for each subject the lowest post-exercise K⁺ concentration was therefore inversely related to the peak K⁺ concentration during exercise. For a given peak K⁺ concentration, the ST subjects had higher plasma K⁺ concentrations than the ET subjects in the recovery period, suggesting that the two groups of subjects may regulate the K⁺ concentration differently after exercise.     

Total body Na-depletion without hyponatraemia can trigger overtraining-like symptoms with sleeping disorders and increasing blood pressure: Explorative case and literature study

Exhausting physical exercise and insufficient nutritional intake impairing immunological and neuro-endocrine pathways are the most discussed issues in research on overtraining syndrome (OTS). Interestingly, depletion of the total body sodium (Na⁺)-content which occurs in case of various diseases with completely different aetiologies is associated with a symptom pattern strikingly comparable to overreaching (OR) and/or OTS. The transient dilution based hyponatraemia gained attention due to its impact on reduced performance and the death of various endurance athletes. But the stepwise depletion of the total body (tissue) Na⁺-content is a completely different pathophysiology and is still relatively unknown. That is because depleted tissue Na⁺-content is hard to detect. The complex, dominant mechanisms for the maintenance of plasma homeostasis are concealing the Na⁺-depletion in the tissues quite successfully in a stage when symptoms already may be prominent. Furthermore, we are all programmed to think about sedentary people who are rather at risk to have a salt (Na⁺) intake which is far too high. But either, competitive top athletes and engaged recreational athletes have high losses of electrolytes with sweat and might be prone to a stepwise Na⁺-depletion. All the more because they also try to have a balanced, health sodium reduced diet. One person of our research group who is used to a rather low sodium-nutrition repeatedly experienced OR-(short term-OTS)-symptoms when training loads of recreational sport activities were increasing. Getting aware about identical symptoms between OR and total body Na⁺-depletion in another professional context the decision for a self experiment was settled. Under a given training protocol changing symptoms under low sodium-nutrition were recorded. When OR-like symptoms became prominent the training loads were maintained but stringent Na⁺-substitution was performed instead of the usually recommended resting period. As experienced before, typical symptoms such as sleeping disorders, harassed feeling, high diuresis, thirst and increasing blood pressure developed within 2 weeks with the increased training loads and the usual low Na⁺-nutrition. This was before plasma sodium decreased below the physiological range. High Na⁺-substitution instead of a resting period enabled the recovery from OR symptoms within some days. Out of various articles we choose and report some interesting further medical phenomenon where our hypothesis of Na⁺-depletion as a trigger mechanism might give new ideas for identifying pathophysiological mechanisms. The hypothesis: Tissue Na⁺-depletion triggers OR- and OTS- development via the renin–angiotensin–aldosterone system which initiate at first a stimulation and then exhaustion of the sympathetic system.     

An 8-Year Longitudinal Study of Overreaching in 114 Elite Female Chinese Wrestlers

Context:Successful training involves structured overload but must avoid the combination of excessive overload and inadequate recovery.Objective:The aim of this study was to determine the incidence of functional overreaching (FOR), nonfunctional overreaching (NFOR), and overtraining syndrome in elite female wrestlers during their normal training and competition schedules and to explore the utility of blood markers for the early detection of overreaching. Classification of FOR, NFOR, and overtraining syndrome was based on the European Congress of Sports Medicine position statement.Design:Case series.Setting:China Institute of Sport Science.Results:Among the 114 athletes, there were 13 (3.6%) instances of FOR, 23 (6.4%) instances of NFOR, and 2 (0.6%) instances of overtraining syndrome. The diagnostic sensitivity for FOR was 38%, 15%, 45%, and 18% for creatine kinase, hemoglobin, testosterone, and cortisol, respectively. The diagnostic sensitivity for NFOR was 29%, 33%, 26%, and 35% for creatine kinase, hemoglobin, testosterone, and cortisol, respectively. Specificity was 79%, 88%, 90%, and 82% for creatine kinase, hemoglobin, testosterone, and cortisol, respectively. Post hoc analysis showed no mean differences in creatine kinase (F = 0.5, P = .47), hemoglobin (F = 3.8, P = .052), testosterone (F = 0.2, P = .62), or cortisol (F = 0.04, P = .85) between monitoring periods when wrestlers were and were not diagnosed with FOR and NFOR.Conclusions:Coaches and sports scientists should not use single blood variables as markers of overreaching in elite female wrestlers.Key Words: blood markers, fatigue, overtraining, underperformance

Key Points

• The incidence of overtraining was high (69%) in world-class female wrestlers.
• The blood variables creatine kinase, hemoglobin, testosterone, and cortisol were not useful markers for the early detection of overreaching.

An imbalance between training stress and recovery is known as overtraining and can result in functional overreaching (FOR), nonfunctional overreaching (NFOR), and overtraining syndrome (OTS).^1,2 Functional overreaching is considered a desirable component of training for elite athletes because of the relatively short recovery time (within 2 weeks) and the associated supercompensatory effect that elicits improved athletic performance.³ In contrast, recovery from NFOR may take several weeks to months and hence has a negative effect on athletes'' training programs. Furthermore, recovery from OTS may take months to years and is characterized by a prolonged decrease in performance, persistent fatigue, and mood disturbances, all of which seriously compromise the competitive athlete.^2,4 The incidence of NFOR and OTS has been estimated to be in the range of 5% to 60% of all athletes during their sports career.^5–9 Therefore, this problem continually needs to be addressed by coaches and scientific support staff. The process of intensified training leading to FOR, NFOR, and OTS is often viewed as a continuum, and the thresholds between these 3 states are extremely narrow. Thus, athletes and coaches need accurate and reliable diagnostic tools to identify overtraining so that timely recovery interventions can be implemented to avoid the negative consequences associated with NFOR and OTS.In the last few decades, considerable research has indicated that FOR, NFOR, and OTS may be identified using diagnostic blood markers,^10–18 physiologic perturbations,^11,16,19,20 and negative changes in the athlete''s psychological state.^{14,16,18,21–23} Most authors who have investigated the early signs of overtraining have relied on deliberately inducing a state of overreaching by exposing athletes to short periods of intensified training.^{10,13,20–23} Such studies, however, rarely reflect the normal training and competition schedules of elite athletes, are difficult to conduct, and raise a variety of ethical concerns. Cross-sectional studies focusing on diagnostic markers of NFOR and OTS generally include athletes from sports medicine clinics in which athletes experiencing OTS are highly represented.^17,18 Unfortunately, such investigations do not reveal any information about the incidence of FOR, NFOR, and OTS during the athletes'' normal training and competition schedules. These studies also do not provide information on the development of FOR and NFOR because they focus on the end stages of the overtraining continuum. Few authors of longitudinal studies have attempted to document the incidence of NFOR and identify early markers of FOR and NFOR within a naturalistic sports setting, and, to the best of our knowledge, no studies have investigated overreaching in elite wrestlers.The main aim of our study was to report the incidence of FOR, NFOR, and OTS in elite female wrestlers, using a longitudinal 8-year observation of the Chinese women''s wrestling team during their normal training and competition schedules. A second aim was to explore the utility of blood markers for the early detection of overreaching.     

Cell numbers and in vitro responses of leucocytes and lymphocyte subpopulations following maximal exercise and interval training sessions of different intensities

Summary In vitro lymphocyte function and the mobilisation of peripheral blood leucocytes was examined in eight trained subjects who undertook an incremental exercise test to exhaustion and a series of interval training sessions. Venous blood samples were obtained before the incremental test, immediately after, and 30, 60, and 120 min after the test. Interval training sessions were undertaken on separate days and the exercise intensities for each of the different sessions were 30%, 60%, 90% and 120% of their maximal work capacity respectively, as determined from the incremental exercise test. There were 15 exercise periods of 1-min duration separated by recovery intervals of 2 min in each session. Venous blood samples were obtained immediately after each training session. Significant increases in lymphocyte subpopulations (CD3⁺, CD4⁺, CD8⁺, CD20⁺, and CD56⁺) occurred following both maximal and supramaximal exercise. This was accompanied by a significant decrease in the response of cultures of peripheral blood lymphocytes to Concanavalin A (ConA), a T-cell mitogen. The state of lymphocyte activation in vivo as measured by CD25⁺ surface antigen was not, however, affected by acute exercise. The total number of lymphocytes, distribution of lymphocyte subpopulations and in vitro lymphocyte response to ConA had returned to pre-exercise levels within half an hour of termination of exercise but serum cortisol concentrations had not begun to fall at this time. There was a significant decrease in the CD4⁺:CD8⁺ cell ratio following exercise; this was more the result of increases in CD3^–CD8⁺ cells (CD8⁺ natural killer cells) than to CD3⁺CD8⁺ cells (CD8⁺ T-lymphocytes). Decreased responsiveness of T-cells to T-cell mitogens, postexercise, may have been the result of decreases in the percentage of T-cells in postexercise mixed lymphocyte cultures rather than depressed cell function. The cause of this was an increase in the percentage of natural killer cells which did not respond to the T-cell mitogen. The results indicated that while a substantial immediate in vitro immunomodulation occurred with acute exercise, this did not reflect an immunosuppression but was rather the result of changes in the proportions of reactive cells in mononuclear cell cultures. We have also demonstrated that the degree of the change in distribution of lymphocyte subpopulation numbers and responsiveness of peripheral blood mononuclear cells in in vitro mitogen reactions increased with increasing exercise intensity. Plasma volume changes may have contributed to some of the changes seen in leucocyte population and subpopulation numbers during and following exercise.     

Total body Na+-depletion without hyponatraemia can trigger overtraining-like symptoms with sleeping disorders and increasing blood pressure: Explorative case and literature study

Exhausting physical exercise and insufficient nutritional intake impairing immunological and neuro-endocrine pathways are the most discussed issues in research on overtraining syndrome (OTS). Interestingly, depletion of the total body sodium (Na⁺)-content which occurs in case of various diseases with completely different aetiologies is associated with a symptom pattern strikingly comparable to overreaching (OR) and/or OTS. The transient dilution based hyponatraemia gained attention due to its impact on reduced performance and the death of various endurance athletes. But the stepwise depletion of the total body (tissue) Na⁺-content is a completely different pathophysiology and is still relatively unknown. That is because depleted tissue Na⁺-content is hard to detect. The complex, dominant mechanisms for the maintenance of plasma homeostasis are concealing the Na⁺-depletion in the tissues quite successfully in a stage when symptoms already may be prominent. Furthermore, we are all programmed to think about sedentary people who are rather at risk to have a salt (Na⁺) intake which is far too high. But either, competitive top athletes and engaged recreational athletes have high losses of electrolytes with sweat and might be prone to a stepwise Na⁺-depletion. All the more because they also try to have a balanced, health sodium reduced diet. One person of our research group who is used to a rather low sodium-nutrition repeatedly experienced OR-(short term-OTS)-symptoms when training loads of recreational sport activities were increasing. Getting aware about identical symptoms between OR and total body Na⁺-depletion in another professional context the decision for a self experiment was settled. Under a given training protocol changing symptoms under low sodium-nutrition were recorded. When OR-like symptoms became prominent the training loads were maintained but stringent Na⁺-substitution was performed instead of the usually recommended resting period. As experienced before, typical symptoms such as sleeping disorders, harassed feeling, high diuresis, thirst and increasing blood pressure developed within 2 weeks with the increased training loads and the usual low Na⁺-nutrition. This was before plasma sodium decreased below the physiological range. High Na⁺-substitution instead of a resting period enabled the recovery from OR symptoms within some days. Out of various articles we choose and report some interesting further medical phenomenon where our hypothesis of Na⁺-depletion as a trigger mechanism might give new ideas for identifying pathophysiological mechanisms. The hypothesis: Tissue Na⁺-depletion triggers OR- and OTS- development via the renin–angiotensin–aldosterone system which initiate at first a stimulation and then exhaustion of the sympathetic system.     

Recovery of heart rate variability after treadmill exercise analyzed by lagged Poincaré plot and spectral characteristics

The aim of this study was to analyze the recovery of heart rate variability (HRV) after treadmill exercise and to investigate the autonomic nervous system response after exercise. Frequency domain indices, i.e., LF(ms²), HF(ms²), LF(n.u.), HF(n.u.) and LF/HF, and lagged Poincaré plot width (SD1 _m ) and length (SD2 _m ) were introduced for comparison between the baseline period (Pre-E) before treadmill running and two periods after treadmill running (Post-E1 and Post-E2). The correlations between lagged Poincaré plot indices and frequency domain indices were applied to reveal the long-range correlation between linear and nonlinear indices during the recovery of HRV. The results suggested entirely attenuated autonomic nervous activity to the heart following the treadmill exercise. After the treadmill running, the sympathetic nerves achieved dominance and the parasympathetic activity was suppressed, which lasted for more than 4 min. The correlation coefficients between lagged Poincaré plot indices and spectral power indices could separate not only Pre-E and two sessions after the treadmill running, but also the two sessions in recovery periods, i.e., Post-E1 and Post-E2. Lagged Poincaré plot as an innovative nonlinear method showed a better performance over linear frequency domain analysis and conventional nonlinear Poincaré plot.     

The influence of weekly training distance on fractional utilization of maximum aerobic capacity in marathon and ultramarathon runners

Summary This study was designed to examine the interrelationships between performance in endurance running events from 10 to 90 km, training volume 3–5 weeks prior to competition, and the fractional utilization of maximal aerobic capacity (% ) during each of the events. Thirty male subjects underwent horizontal treadmill testing to determine their , and steady-state at specific speeds to allow for calculation of % sustained during competition. Runners were divided into groups of ten according to their weekly training distance (group A trained less than 60 km · week^–1, group B 60 to 100 km · week^–1, and group C more than 100 km · week^–1). Runners training more than 100 km · week^–1 had significantly faster running times (average 19.2%) in all events than did those training less than 100 km · week^–1. or % sustained during competition was not different between groups. The faster running speed of the more trained runners, running at the same % during competition, was due to their superior running economy (19.9%). Thus all of the group differences in running performance could be explained on the basis of their differences in running economy. These findings suggest either that the main effect of training more than 100 km · week^–1 may be to increase running economy, or that runners who train more than 100 km · week^–1 may have inherited superior running economy. The finding that the maximal horizontal running speed reached during the progressive maximal treadmill test was a better predictor (r=0.72) of running performance at all distances than was the (r=0.54) suggests that peak treadmill running speed can predict performance in endurance running events.     

Effect of 6 weeks of sprint training on growth hormone responses to sprinting

This study examined the effect of 6 weeks of prescribed sprint training on the human growth hormone (hGH) response to cycle ergometer sprinting. Sixteen male subjects were randomly assigned to a training (n=8) or a control (n=8) group. Each subject completed two main trials, consisting of two all-out 30-s cycle-ergometer sprints separated by 60 min of passive recovery, once before, and once after a 6-week training period. The training group completed three supervised sprint-training sessions per week in addition to their normal activity, whilst control subjects continued with their normal activity. In the training group, peak and mean power increased post-training by 6% (P<0.05) and 5% (P<0.05), respectively. Post-exercise blood pH did not change following training, but the highest post-exercise blood lactate concentrations were greater [highest measured value: 13.3 (1.0) vs 15.0 (1.1) mmol l^–1], with lower blood lactate concentrations for the remainder of the recovery period (P<0.05). Post-exercise plasma ammonia concentrations were lower after training [mean highest measured value: 184.1 (9.8) vs 139.0 (11.7) mol l^–1, P<0.05]. Resting serum hGH concentrations did not change following training, but the peak values measured post-exercise decreased by over 40% in the training group [10.3 (3.1) vs 5.8 (2.5) g l^–1, P<0.05], and mean integrated serum hGH concentrations were 55% lower after training [567 (158) vs 256 (121) min g l^–1, P<0.05]. The hGH response to the second sprint was attenuated similarly before and after training. This study showed that 6 weeks of combined speed- and speed-endurance training blunted the human growth hormone response to sprint exercise, despite an improvement in sprint performance.     

The colon carcinoma cell line Caco-2 contains an H+/K+-ATPase that contributes to intracellular pH regulation

The presence of an H⁺/K⁺-ATPase and its contribution to the regulation of intracellular pH (pH_i) was investigated in Caco-2 cells. The H⁺/K⁺-ATPase was detected immunologically using the monoclonal antibody 5-B6, which was raised against hog gastric H⁺/K⁺-ATPase. Cell pH was determined using the pH-sensitive dye 2,7-bis(carboxyethyl)-carboxyfruorescein. Control pH_i, measured in HCO ₃ ^– -free medium, was 7.62±0.03 (n=27) when cells were cultured for 14 days and decreased to 7.40±0.03 (n=18) after 35 days in culture. Recovery of pH_i following a NH ₄ ⁺ /NH₃ pulse could be reduced by either 100 M SCH 28080 or 1 mM amiloride, or by removing extracellular Na⁺. The inhibitory effects of SCH 28080 and amiloride were additive, demonstrating the involvement of a gastric-like H⁺/K⁺-ATPase and a Na⁺/H⁺ exchanger in regulating pH_i. Recovery rates at pH_i 6.8 were not significantly different in cells cultured for up to 21 days, but were significantly lower in cells cultured for 28 and 35 days. This decrease in recovery rate was due to a decrease in the SCH-28080-insensitive recovery, indicating a reduction of the relative importance of Na⁺/H⁺ exchange to the recovery. Recovery of pH_i was also inhibited by 1 mM N-ethylmaleimide. However, it is unlikely that N-ethylmaleimide inhibited a vacuolar type of H⁺-ATPase, since bafilomycin A₁ had no effect on pH_i recovery. In conclusion, Caco-2 cells contain a SCH-28080-sensitive mechanism for regulating pH_i, which is most conveniently studied after 28 days in culture, when the relative contribution of a Na⁺/H⁺ exchanger to pH_i regulation is decreased.     

The effects of altered exercise distribution on lymphocyte subpopulations

The effects of exercise distribution on lymphocyte count, lymphocyte subpopulations and plasma cortisol concentration in peripheral blood were assessed in 19 healthy subjects. The subjects were randomly divided into group A (n = 10) or group B (n = 9) according to exercise distribution. Both groups underwent a 10-week programme involving 5 × 2-week blocks: baseline (B), training period 1 (TP1), stabilisation 1 (S1), training period 2 (TP2), and stabilisation 2 (S2). During B, S1 and S2 normal training was undertaken. During TP1 and TP2 the subjects increased the amount of training by 50% in week 1 and by 100% in week 2. During TP1 subjects in group A exercised 6 days·week^–1, while during TP2 these subjects exercised on 3 alternate days·week^–1, but doubled the duration of each training session. The subjects in group B reversed this training order. Blood was collected 36–42 h following exercise period B, and at the end of periods TP1, S1, TP2 and S2, and also 12–18 h following completion of exercise at the end of TP1 and TP2. There were no significant differences (P > 0.05) between the 6 day·week^–1 programme and the 3 alternate day·week^–1 programme in total lymphocyte count, CD3⁺, CD4⁺, CD8+, CD16⁺, or CD19⁺ cells, the CD4:CD8 ratio, HLA-DR⁺ (activated) T cells or plasma cortisol concentrations. Following both TP1 and TP2 there was a nonsignificant decrease in lymphocyte subpopulations. However following both S1 and S2 (baseline training) there was a significant increase in total lymphocyte count, CD3⁺, CD4⁺ and CD8⁺ lymphocytes. The S2 variables statistically significant from B were: total lymphocyte count (P < 0.01), CD3⁺ T-cells and percentage of circulating lymphocytes (^P < 0.01), CD4⁺ cells (P < 0.0001), CD8⁺ cells (P < 0.05), and HLA-DR⁺ (activated) T-cells (P < 0.05). The results indicated that provided the amount of exercise is constant for a given period, then exercise distribution is not a critical variable in the alteration of lymphocyte subpopulations that may occur in response to overload training. However 2 weeks of overload training followed by 2 weeks of active recovery (baseline) training may induce an increase in the lymphocyte count.     

Influence of training on the response of androgen plasma concentrations to exercise in swimmers

In eight top-level male endurance swimmers the aerobic performance and the response to exercise of total testosterone (T), free testosterone (fT), sex hormone binding globulin (SHBG), non-SHBG-bound testosterone (NST) and cortisol (C) were evaluated during a training season. The swimmers participated in three test sessions which occurred 6, 12 and 24 weeks after the beginning of the season. During each session, after a standard warm-up, the swimmers performed a set of 15 × 200-m freestyle, with a 20-s rest between repetitions, at a predetermined individual speed. Three blood samples were collected: before warm-up, at the end of the set, and after 1 h of recovery. A few days before each session, the individual swimming velocity associated with a 4 mmol · l^–1 blood lactate concentration (₄) was assessed as a standard of aerobic performance. The values of ₄ were lower in the second session than in the third one. The concentrations of C, which increased after the exercise, showed the highest values in the second session. The values of T and the T: SHBG ratio increased after the exercise but returned to their initial concentrations during the recovery period. The values of fT and NST increased after the exercise in the first and third sessions. In the initial two sessions, when the aerobic performance was still low, the concentrations of NST decreased to below the initial values after recovery. In session III, when the adaptation to the training workload was complete, NST returned to resting concentrations after recovery. The results would suggest that stressful stimuli produced by an increase in training volume may induce changes in androgen metabolism during exercise. In this respect, NST would appear to be a better index of metabolic response than T, T/SHBG and fT.     

Changes in the concentrations of Na+, K+ and Cl− in secretion from the skin during progressive increase in exercise intensity

Summary A simple method for sampling skin secretion in 1-min periods was developed for investigating the effects of progressive increases in exercise intensity on Na⁺, K⁺ and CI^– secretions from the skin of the forearm. Ten healthy male subjects performed exercise consisting of eight stepwise increases in intensity from 50 to 225 W, with a 25-W increase at each step. Exercise at each step was for 3 min followed by a 1-min recovery period. Samples of blood and skin secretion were taken during the recovery period. Significant positive correlations were found between the mean concentrations of Na⁺ and Cl^– and between those of K⁺ and Cl^– in the skin secretion. The concentrations of electrolytes in the skin secretion also showed significant correlations with the blood lactate concentrations. The inflection points for secretions of Na⁺, K⁺ and Cl^– were 4.04, 3.61 and 3.83 mmol · l^– of blood lactate; 64.42, 61.96 and 62.14% of maximal oxygen consumption ( ); and exercise intensities of 123.01, 117.65 and 125.07 W, respectively. No significant differences were observed between the value of 67.27% of or 134.00W at the onset of blood lactate accumulation (OBLA) and the inflection points. From these results we concluded that changes in electrolyte concentrations in skin secretion during incremental exercise according to this protocol were closely related with the change in the blood lactate concentration, and that the inflection points for electrolytes may have been near the exercise intensity at OBLA.     

Exposure to a rotating virtual environment during treadmill locomotion causes adaptation in heading direction

The objective of this study was to investigate the adaptive effects of variation in the direction of optic flow, experienced during linear treadmill walking, on modifying locomotor trajectory. Subjects (n=30) walked on a motorized linear treadmill at 4.0 km h^–1 for 24 min while viewing the interior of a 3D virtual scene projected on to a screen 1.5 m in front of them. The virtual scene depicted constant self-motion equivalent to either (1) walking around the perimeter of a room to ones left (Rotating Room group) or (2) walking down the center of a hallway (Infinite Corridor group). The scene was static for the first 4 min and then constant rate self-motion was simulated for the remaining 20 min. Before and after the treadmill locomotion adaptation period subjects performed five stepping trials. In each trial they marched in place to the beat of a metronome at 90 steps min^–1 for a total of 100 steps while blindfolded in a quiet room. The subjects final heading direction (deg) and final X (fore–aft, cm) and final Y (medio-lateral, cm) positions were measured for each trial. During the treadmill locomotion adaptation period subjects 3D torso position was measured. We found that subjects in the Rotating Room group, as compared with the Infinite Hallway group: (1) showed significantly greater deviation during post-exposure testing in the heading direction and Y position opposite to the direction of optic flow experienced during treadmill walking; and (2) showed a significant monotonically increasing torso yaw angular rotation bias in the direction of optic flow during the treadmill adaptation exposure period. Subjects in both groups showed greater forward translation (in the +X direction) during the post-treadmill stepping task that differed significantly from their pre-exposure performance. Subjects in both groups reported no perceptual deviation in position during the stepping tasks. We infer that viewing simulated rotary self-motion during treadmill locomotion causes adaptive modification of sensorimotor integration in the control of position and trajectory during locomotion, which functionally reflects adaptive changes in the integration of visual, vestibular, and proprioceptive cues. Such an adaptation in the control of position and heading direction during locomotion, because of the congruence of sensory information, demonstrates the potential for adaptive transfer between sensorimotor systems and suggests a common neural site for processing and self-motion perception and concurrent adaptation in motor output.     

Leptin as a marker of training stress in highly trained male rowers?

The purpose of this study was to investigate the potentially important role leptin may play during training monitoring in athletes. Twelve highly trained male rowers underwent a 3-week period of maximally increased training stress followed by a 2-week tapering period. Fasting blood was sampled after a rest day. Subjects also performed a maximal 2000-m rowing ergometer test before and after 3 weeks of heavy training, and after 2 weeks of tapering. Blood samples were obtained before, immediately after and after 30 min of recovery. Leptin concentrations were measured in duplicate by radioimmunoassay. Mean training time was about 100% higher during the heavy training period (17.5 h·week^–1) compared to the tapering period (8.9 h·week^–1). The 3-week heavy training period induced a significant reduction (P<0.05) in the fasting leptin concentration [from 2.5 (0.4) to 1.5 (0.4) ng·ml^–1]. Fasting plasma leptin was significantly increased by the end of the 2-week tapering period [2.0 (0.4) ng·ml^–1] but remained significantly lower compared to the pretraining value. Leptin levels were also significantly decreased only after the 2000-m rowing ergometer test performed at the end of the heavy training period. No differences in leptin concentrations were observed after other performance tests compared to their respective baseline values. In addition, fasting leptin concentration was significantly related to the weekly training time (r=–0.45; P=0.006). In conclusion, it appears that leptin is sensitive to the rapid and pronounced changes in training volume. A greater training time is associated with a lower leptin concentration in highly trained male rowers. It is suggested that it may be possible to direct typical rowing training by monitoring leptin status.     

Effect of restricted potassium intake on its excretion and on physiological responses during heat stress

Summary The effect of low potassium (K⁺) intake on its excretion, concentration in sweat and on physiological responses during heat stress was evaluated on eight Indian male soldiers in winter months at Delhi. After a stabilization period of 3 days on each diet, i.e., 85 mEq of K⁺/d (diet I, normal), 55 mEq of K⁺/d (diet II), and 45 mEq of K⁺/d (diet III), the physiological responses and the sodium and potassium concentrations in sweat, plasma, RBC, and urine were measured when the subjects were exposed to heat for 3 h daily in a climatic chamber maintained at 40 C DB and 32 C WB. The subjects worked in the chamber at the rate of 465 W/h for 20 min periods with 40 min rest between each period of exercise. The whole body sweat was collected after the first spell of work and was analysed for sodium and potassium levels.Throughout the study the subjects remained on positive sodium balance except on day 4 in diet III. Fluid balance also remained positive while potassium balance was negative in subjects on diet II and diet III. There was no significant change in heart rate, sweat volume, oral temperature, sodium, and potassium concentrations in plasma and RBC during the entire period of the study. Even in the subjects with negative potassium balance there was no change in the sodium and potassium concentrations in sweat during exercise in heat. The only evidence of potassium conservation was a reduced excretion in urine. Out of the eight subjects, in one subject there was a flattening of the T wave in the ECG and reduction in amplitude of the T wave in two more subjects. As there is no reduction in sweat potassium concentration and the urine volume is low, the marginal level of reduced excretion of potassium in urine with a high rate of sweating (7–81) in subjects doing work in the tropics, there is every likelihood of potassium deficiency if a liberal intake is not ensured.     

Relationship between ventilation and arterial potassium concentration during incremental exercise and recovery

Summary The purpose of this study was to compare the relationship of ventilation ( _E) with pH, arterial concentrations of potassium ([K⁺]_a), bicarbonate ([HCO₃ ^–]_a), lactate ([la]_a), and acid-base parameters which would affect hyperpnoea during exercise and recovery. To assess this relationship, ten healthy male subjects exercised with intensity increasing as a ramp function of 20 W · min^–1 until voluntary exhaustion and they were then allowed a 5-min recovery period. Breath-by-breath gas exchange data, [HCO₃ ^–]_a, pH, [1a]_a, [K⁺]_a and blood gases were determined during both exercise and recovery. Using a linear regression method, the _E/[K⁺]a relationship was analysed during both exercise and recovery. Several interesting results were obtained: a significant relationship between [K⁺]_a and _E was observed during recovery as well as during exercise; the _E at any given values of [K⁺]_a was significantly higher during recovery than during exercise and out of those factors affecting exercise hyperpnoea, only [K⁺]_a had a similar time-course to _E during recovery. Changes in [K⁺]a during recovery were shown to occur significantly faster than _E with an [K⁺]_a time constant of 70.0 s, SD 16.2 as opposed to 105.5 s, SD 10.0 for _E (P < 0.01). These results provided further evidence that [K⁺]_a might play an important role as a substance which can stimulate exercise hyperpnoea as has been suggested by other workers. The present study also showed that during recovery [K⁺]_a contributed significantly to the control of _E.     

Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players

Context

Good sleep is an important recovery method for prevention and treatment of overtraining in sport practice. Whether sleep is regulated by melatonin after red-light irradiation in athletes is unknown.

Objective

To determine the effect of red light on sleep quality and endurance performance of Chinese female basketball players.

Design

Cohort study.

Setting

Athletic training facility of the Chinese People''s Liberation Army and research laboratory of the China Institute of Sport Science.

Patients or Other Participants

Twenty athletes of the Chinese People''s Liberation Army team (age = 18.60 ± 3.60 years) took part in the study. Participants were divided into red-light treatment (n = 10) and placebo (n = 10) groups.

Intervention(s)

The red-light treatment participants received 30 minutes of irradiation from a red-light therapy instrument every night for 14 days. The placebo group did not receive light illumination.

Main Outcome Measure(s)

The Pittsburgh Sleep Quality Index (PSQI) questionnaire was completed, serum melatonin was assessed, and 12-minute run was performed at preintervention (baseline) and postintervention (14 days).

Results

The 14-day whole-body irradiation with red-light treatment improved the sleep, serum melatonin level, and endurance performance of the elite female basketball players (P < .05). We found a correlation between changes in global Pittsburgh Sleep Quality Index and serum melatonin levels (r = −0.695, P = .006).

Conclusions

Our study confirmed the effectiveness of body irradiation with red light in improving the quality of sleep of elite female basketball players and offered a nonpharmacologic and noninvasive therapy to prevent sleep disorders after training.Key Words: Pittsburgh Sleep Quality Index, melatonin, 12-minute run

Key Points

• Red-light illumination positively affected sleep quality and endurance performance variables in Chinese female basketball players.
• Red-light illumination is a positive nonpharmacologic and noninvasive therapy to prevent sleep disorders after training.

Good sleep is a prerequisite for optimal performance.¹ Given that people spend about one-third of their lives asleep, sleep has substantial functions for development, daily functioning, and health.² Perhaps no daytime behavior has been associated more closely with improved sleep than exercise.³ Researchers have shown that exercise serves as a positive function for sleep. Regular exercise consistently has been associated with better sleep.⁴ Moreover, the American Academy of Sleep Medicine considers physical exercise to be a modality of nonpharmacologic treatment for sleep disorders.⁴ When studying the influence of exercise on sleep, most investigators have compared acute exercise and sedentary control treatments.⁵ In their study of chronic moderate-intensity endurance exercise, Driver and Taylor⁶ also provided compelling evidence that exercise promotes sleep.However, exercise can negatively affect sleep quality. Exercising immediately before going to sleep is detrimental to sleep quality.⁷ Athletes train very hard to improve their on-field performances, but excessive training may lead to a decrease in performance, which is known as overtraining syndrome. Researchers⁸ have shown that symptoms of overtraining indicate poor-quality sleep. Good sleep is an important recovery method for prevention and treatment of overtraining in sport practice.⁹Evidence is compelling that chronic exposure to bright light (3000 lux) can enhance sleep.¹⁰ Guilleminault et al¹¹ suggested that the effects of exposure to light may be more powerful than those associated with exercise. In a recent study in which red-light therapy (wavelength = 670 nm, light dose = 4 J/cm²) was used, Yeager et al¹² indicated that red light could restore glutathione redox balance upon toxicologic insult and enhance both cytochrome c oxidase and energy production, all of which may be affected by melatonin. Melatonin is a neurohormone that is produced by the pineal gland and regulates sleep and circadian functions.¹³ No one knows whether sleep is regulated by melatonin after red-light irradiation in athletes. Researchers^14,15 have demonstrated that phototherapy improves muscle regeneration after exercise. Red light could protect human erythrocytes in preserved diluted whole blood from the damage caused by experimental artificial heart-lung machines.¹⁶ However, the effect of red-light illumination on endurance performance is a new topic in sport science.Sleep quality can be defined subjectively by self-report¹⁷ or by more objective measures, such as polysomnography or actigraphy.¹⁸ Subjective sleep quality has been assessed most widely with the Pittsburgh Sleep Quality Index (PSQI).¹⁷ The PSQI is a comprehensive 18-item self-report questionnaire assessing sleep disturbances in the previous month. It derives ordinal scores for 7 clinically relevant domains of sleep: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances (eg, awakenings from sleep due to discomfort, bad dreams), use of sleeping medication, and daytime dysfunction (feeling sleepy during the day due to a poor night''s sleep). Scores from these separate components are combined to derive a global measure of sleep quality.¹⁹As demonstrated in these studies, acute or chronic exercise may lead to good- or bad-quality sleep. However, the effects of red light on sleep quality and endurance performance have not been investigated sufficiently. Therefore, the purpose of our study was to determine the effect of red light on the sleep quality and endurance performance of Chinese female basketball players.     

Muscle energetics in short-term training during hypoxia in elite combination skiers

Four well-trained combination skiers were studied through pre- and post-training for the effects of short-term intermittent training during hypoxia on muscle energetics during submaximal exercise as measured by Phosphorus-31 nuclear magnetic resonance and maximal aerobic power ( O_2max). The hypoxia and training in the cold was conducted in a hypobaric chamber and comprised 60-min aerobic exercise (at an intensity equivalent to the blood lactate threshold), using a cycle ergometer or a treadmill twice a day for 4, consecutive days at 5°C, in conditions equivalent to an altitude of 2000 m (593 mm Hg). No change in O_2max was observed over the training period, while in the muscle energetics during submaximal exercise, the values of phosphocreatine/(phosphocreatine + inorganic phosphate) and intracellular pH were found to be significantly increased by training during hypoxia. During recovery, the time constant of phosphocreatine was found to have been significantly reduced [pre, 27.9 (SD 6.7) s; post, 22.5 (SD 4.7) s, P < 0.01]. The observed inhibition of phosphocreatine as well as that of intracellular pH changes after training during hypoxia and quicker recovery of phosphocreatine in submaximal exercise tests, may indicate improved oxidative capacity (i.e. a high adenosine 5-triphosphate formation rate) despite the short-term hypoxia training. Present address: Department Life Sciences, Univ. of Tokyo, Komaba 3-8-1, Meguro-ku 153, Japan     

Walking performance and economy in chronic heart failure patients pre and post exercise training

The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8 (SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for 15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake ( O_2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O_2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml?·? kg^–1?·?min^–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m?·?s^–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W?·?kg^–1] had increased (P?–1?·? m^–1] had decreased (P?相似文献