Determining V̇O2max in competitive swimmers: Comparing the validity and reliability of cycling, arm cranking, ergometer swimming, and tethered swimming

OBJECTIVES

This study aims to identify the optimal method for determining V̇O2max in competitive swimmers in terms of validity and test-retest reliability.

DESIGN

Controlled experiment.

METHODS

Twenty competitive swimmers performed four maximal incremental exercise tests: cycling, arm cranking, ergometer swimming, and tethered swimming. Gas analysis was conducted to estimate V̇O2max. Validity was assessed in terms of the amount of variance of the performance on a 1500-m time trial explained by the estimated V̇O2max . Test-retest reliability was evaluated using the intraclass correlation coefficient (ICC).

RESULTS

V̇O2max obtained from tethered swimming, ergometer swimming, and cycling explained a similar amount of variance of the 1500-m performance (R2 = 0.64, 0.64 and 0.65, respectively). However, ergometer swimming yielded significantly lower V̇O2max estimates (40.54 ± 6.55 ml/kg/min) than tethered swimming (54.40 ± 6.21 ml/kg/min) and cycling (54.39 ± 5.63 ml/kg/min). Arm cranking resulted in both a lower explained variance (R2 = 0.41) and a significantly lower V̇O2max (43.14 ± 7.81 ml/kg/min). Tethered swimming showed good reliability (ICC = 0.81).

CONCLUSIONS

Bicycle and tethered swimming tests demonstrated high validity with comparable V̇O2max estimates, explaining a large proportion of differences in endurance performance. Choosing between these two methods involves a trade-off between a higher practical applicability and reliability of the bicycle test and the more sport-specific nature of the tethered swimming test.

Dietary Supplementation with Lauric Acid Improves Aerobic Endurance in Sedentary Mice via Enhancing Fat Mobilization and Glyconeogenesis

BACKGROUND

Lauric acid (LA), a major, natural, medium-chain fatty acid, is considered an efficient energy substrate for intense exercise and in patients with long-chain fatty acid β-oxidation disorders. However, few studies have focused on the role of LA in exercise performance and related glucolipid metabolism in vivo.

OBJECTIVES

We aimed to investigate the effect of dietary supplementation with LA on exercise performance and related metabolic mechanisms.

METHODS

Male C57BL/6N mice (14 wk old) were fed a basal diet or a diet containing 1% LA, and a series of exercise tests, including a high-speed treadmill test, aerobic endurance exercises, a 4-limb hanging test, and acute aerobic exercises, were performed.

RESULTS

Dietary supplementation with 1.0% LA accelerated the recovery from fatigue after explosive exercise (P < 0.05) and improved aerobic endurance and muscle strength in sedentary mice (P = 0.039). Lauric acid intake not only changed muscle fatty acid profiles, including increases in C12:0 and n-6/n-3 PUFAs (P < 0.001) and reductions in C18:0, C20:4n-6, C22:6n-3, and n-3 PUFAs (P < 0.05) but also enhanced fat mobilization from adipose tissue and fatty acid oxidation in the liver, at least partly via the AMP-activated protein kinase-acetyl CoA carboxylase pathway (P < 0.05). Likewise, LA supplementation promoted liver glyconeogenesis and conserved muscular glycogen during acute aerobic exercise (P < 0.05), which was accompanied by an increase in the mitochondrial DNA copy number and Krebs cycle activity in skeletal muscle (P < 0.05).

CONCLUSIONS

Dietary supplemental LA serves as an efficient energy substrate for sedentary mice to improve aerobic exercise endurance and muscle strength through regulation of glucolipid metabolism. These findings imply that LA supplementation might be a promising nutritional strategy to improve aerobic exercise performance in sedentary people.

Effect of Lactate Minimum Speed-Guided Conditioning on Selected Blood Parameters of Horses

During exercise, equines can suffer severe water and electrolyte imbalances depending on the intensity and duration. In this sense, conditioning aims to promote adaptations to the organism in order to maintain cardiovascular and thermoregulatory stability during exertion. This study aimed to evaluate the effect of conditioning guided by lactate minimum speed (LMS) test on the blood osmolality of horses. We hypothesized that after conditioning the blood osmolality would vary less during exercise and that LMS could be used in equine conditioning program. Ten Arabian horses were evaluated before (ET 1) and after (ET 2) 6 weeks of conditioning. The conditioning intensity was established from the LMS during ET 1. The blood was obtained at rest and during the ETs. An increase in LMS and a decrease in lactate were seen in individual horses; however, these differences were not significant at a group level. No change in blood osmolality was observed when comparing the ETs. The plasma volume remained unchanged in ET 2. The conditioning guided by LMS improved the animals' fitness, which was evidenced by the lower lactate production in ET 2. The fact that the osmolality kept unchanged proves the effectiveness of the osmotic blood balance during exercise, as its control involves the interaction of different systems. Body adaptations occurred with conditioning, providing greater homeostasis control since the plasma volume remained stable in ET 2. It was concluded that the LMS test can be used to define an effective equine conditioning program even though some adjustments are still necessary.

Glittre endurance test: A new test to assess the functional capacity of individuals with chronic obstructive pulmonary disease

BACKGROUND

For people with chronic obstructive pulmonary disease (COPD) the ability to perform functional activities for a prolonged duration is important for completion of daily tasks. While the Glittre-ADL test measures time taken to complete a series of functional activities, there is no test of endurance capacity for common daily activities.

RESEARCH QUESTION

Is the Glittre Endurance test a valid and responsive test to measure endurance capacity for functional daily tasks in people with COPD?

METHODS

This was a cross-sectional study. Fifty-seven participants with COPD (mean ± SD age:69 ± 7 years; FEV₁:48 ± 18%predicted) were recruited. All participants performed the Glittre-ADL test without a backpack (Glittre-ADL-noBP). Nine participants (Group A) performed a Glittre Endurance test at 90% of the speed to complete one lap of the Glittre-ADL-noBP. 48 participants (Group B) performed two Glittre Endurance tests at 100% of Glittre-ADL-noBP speed. The time to voluntary cessation or not keeping up with target pace was the test outcome.

RESULTS

Mean ± SD of the Glittre Endurance test was 12.11 ± 6.43 min and 6.90 ± 4.40 min for the test at 90% and 100% speeds, respectively. When the 100% Glittre Endurance test 2 was compared to test 1, there was a 14% increase in test time, indicating a learning effect (p = 0.005). Following pulmonary rehabilitation (n = 20) the Glittre Endurance test increased by 3.12 min (29%), and the Glittre-ADL-noBP reduced by 0.33 min (10%).

CONCLUSION

The Glittre Endurance test performed at 100% of the Glittre-ADL-noBP speed provided an appropriate endurance test time, and was more sensitive to change following pulmonary rehabilitation than the Glittre-ADL-noBP.

Comparative evaluation for recycling waste power batteries with different collection modes based on Stackelberg game

The new energy vehicle industry is booming, but the subsequent problem of vehicle power batteries' "scrap tide" is still severe. How to establish and improve the end-of-life power battery recycling system to avoid the "catastrophic" environmental consequences has become an urgent global problem needing a solution. This article constructs three recycling models for manufacturer recycling, retailer recycling, and mixed recycling. By using Stackelberg game and market real data, the influence of carbon trading policy outside the supply chain, power battery endurance capacity and advertising effects within the supply chain on the selection of recycling channels was studied. The results showed: (1) Different recycling channels did not affect the wholesale price, retail price, and market demand for raw material power batteries in the positive supply chain; (2) The total profit function of manufacturers and retailers had a "U-shaped" non-linear relationship with power battery endurance capacity and has a positive linear relationship with the advertising effect. Taking the R&D endurance capacity of 0.4 and the total endurance capacity of 62 kWh as the lowest dividing point, it will decrease first and then increase; (3) The increase in the recycling competition coefficient had a greater impact on the consumption of carbon emission rights in the mixed recycling model than on savings in carbon emission rights, and retailers were the indirect "victims" of rising carbon trading prices; (4) Endurance capacity, advertising effects, and carbon trading prices determined the economics of the recycling model and the carbon emission reduction potential. Manufacturers, retailers, and governments can refer to the value range of each variable to select the most appropriate recycling mode.

Psychophysical condition of adolescents in coronavirus disease 2019

This study investigated the prevalence of depression and levels of physical fitness in high school students during the coronavirus disease 2019 (COVID-19) pandemic. One hundred fifty participants were divided into four groups according to the number of days that they felt depressed due to the COVID-19 during the last 7 days: no-depression group (NDG, n=17), some-depression group (SDG, n=32), occasional-depression group (ODG, n=81), and most-depression group (MDG, n=20). Shuttle run for endurance capacity and standing long jump for muscle power were selected to estimate the states of type I and type II muscle fibers, respectively. This study found that the Center for Epidemiologic Studies Depression Scale score of MDG was significantly higher than those of other three groups. In addition, ODG and MDG showed the lowest interest in their school studies compared with other groups. Endurance capacity showed a significant difference among groups, whereas muscle power showed no significant difference among groups. In conclusion, this study suggests that higher levels of depression reflect a greater lack of interest in life and academics. Furthermore, lower endurance capacity appears to be associated with more severe levels of depression. This highlights the importance of maintaining type I muscle fibers through regular aerobic exercise.

Portable NIV for patients with moderate to severe COPD: two randomized crossover trials

BACKGROUND

Long-term non-invasive ventilation (NIV) is as an established treatment option for chronic hypercapnic COPD patients. Beneficial effects have also been shown during exercise, but this is restricted to rehabilitation programs. New portable NIV (pNIV) devices may now enable NIV application during walking at home.

STUDY DESIGN AND METHODS

In two randomized crossover trials, the impact of pNIV on dyspnea and endurance capacity was investigated in patients with moderate to severe COPD. Participants performed a standardized 6-min walking test, with and without pNIV, using a pre-set inspiratory/expiratory positive airway pressure of 18/8 cmH₂O. The first study was performed in NIV-naïve patients (Study I), while the second study was performed in those already established on long-term NIV (Study II).

RESULTS

38 patients (66.9 ± 7.4 years, mean FEV₁: 30.3 ± 8%pred) and 23 patients (67.6 ± 8.7 years, mean FEV₁: 29.8 ± 10.4%pred) participated in Study I and II, respectively. In Study I, the mean difference in the Borg Dyspnea Scale (BDS, primary outcome) score following walking was 3.2 (IQR 2-4) without pNIV, compared to 2.6 (IQR 1-4) with pNIV (ΔBDS 0.65, P = 0.04), while walking distance increased from 311.8 m (95%CI 276.9-346.6 m) to 326.3 m (95%CI 291.5-361.2 m) (P = 0.044) when pNIV was used. Accordingly, in Study II, the mean difference in BDS was 4.4 (IQR 3-6) without pNIV, compared to 4.5 (IQR 3-6) with pNIV (ΔBDS 0.09, P = 0.54), while walking distance decreased from 291.5 m (95%CI 246.1-336.9 m) to 258.4 m (95%CI 213-303.8 m) (P ≤ 0.001).

INTERPRETATION

The use of a pNIV device during walking can improve dyspnea and walking distance in patients with moderate to severe COPD. Patients who do not already receive long-term NIV therapy are more likely to benefit compared to those undergoing long-term NIV. Careful patient selection is mandatory. Clinical Trial Register: DRKS00013203; DRKS00012913 registered October 20th 2017 and October 16th 2017; https://www.drks.de/drks_web/.

Towards Optimized Care After Bariatric Surgery by Physical Activity and Exercise Intervention: a Review

Although there is growing evidence on the importance of physical activity and exercise intervention after bariatric surgery, it remains to be clarified as to why and how post-operative exercise intervention should be implemented. In this narrative and practically oriented review, it is explained why exercise interventions and physical activity are important after bariatric surgery, how to prescribe exercise and monitor physical activity and how and when physical fitness, muscle strength, fat (-free) mass and bone mineral density could be assessed during follow-up. It is suggested that the inclusion of physical activity and exercise training in the clinical follow-up trajectory could be of great benefit to bariatric surgery patients, since it leads to greater improvements in body composition, bone mineral density, muscle strength and physical fitness.

Endurance training during maintenance hemodialysis in pediatric and adolescent patients-theory and best practice suggestions

Patients on maintenance hemodialysis (HD) spend significant sedentary time traveling to and receiving dialysis, which leaves little time for social or sport events. Also, chronic HD patients are not physically fit, too exhausted after HD, and are not necessarily motivated to perform sports. There is increasing evidence that endurance training during HD can both increase dialysis efficacy and improve the ability of patients to participate in social life. With limited spare time, how can we motivate patients to train? Would that training improve endurance and modify leisure activity choice? Since HD patients would be a captive audience, we would suggest that endurance training during HD would be a preferred solution, if pediatric and adolescent patients could be persuaded to participate. There are few data on how training should be organized, as well as which parameters are best markers of safety and efficacy. And, most importantly, motivational aspects for performing endurance training on a regular basis clearly have to be considered. It is therefore in any case important to assess whether training improves endurance and, thus, quality of life or also quality of care parameters.

Effects of Rhodiola rosea supplementation on mental performance, physical capacity, and oxidative stress biomarkers in healthy men

PURPOSE

The objective of this study was to investigate the effects of chronic Rhodiola rosea (R. rosea) supplementation on mental and physical performance, as well as hormonal and oxidative stress biomarkers.

METHODS

Twenty-six healthy male students received either R. rosea extract (600 mg/day; RR) or placebo (PL) in a randomized double-blind trial. Prior to supplementation (Term I) and following 4 weeks of supplementation (Term II), the students underwent psychomotor tests for simple and choice reaction time, included in the Vienna Test System. Also, the subjects performed VO_2peak test. Blood samples were obtained before and after the test to measure the hormonal profile (cortisol, testosterone, and growth hormone), as well as the biomarkers of oxidative stress (lipid hydroperoxides, total antioxidant capacity, and superoxide dismutase) and muscle damage (creatine kinase).

RESULTS

R. rosea ingestion shortened reaction time and total response time. Moreover, a greater relative increase in the number of correct responses was observed in RR group as compared to the PL group. No changes in endurance exercise capacity and hormonal profile were observed after R. rosea ingestion. R. rosea ingestion raised plasma total antioxidant capacity. It did not, however, affect other measured parameters.

CONCLUSION

Chronic R. rosea ingestion does not affect physical performance, but can improve the results of some psychomotor tests (simple and choice reaction time) in young, healthy, and physically active men. The improvements in mental performance, however, at least in our study, seem not to be related to changes in cortisol release or antioxidant activity of R. rosea extract. Thus, the specific mechanisms responsible for these effects still need to be elucidated.

Muscle morphology and performance in master athletes: A systematic review and meta-analyses

INTRODUCTION

The extent to which chronic exercise training preserves age-related decrements in physical function, muscle strength, mass and morphology is unclear. Our aim was to conduct a systematic review of the literature to determine to what extent chronically trained master athletes (strength/power and endurance) preserve levels of physical function, muscle strength, muscle mass and morphology in older age, compared with older and younger controls and young trained individuals.

METHODS

The systematic data search included Medline, EMBASE, SPORTDiscus, CINAHL and Web of Science databases.

INCLUSION CRITERIA

i) master athletes mean exercise training duration ≥20 years ii) master athletes mean age of cohort >59 years) iii) at least one measurement of muscle mass/volume/fibre-type morphology and/or strength/physical function.

RESULTS

Fifty-five eligible studies were identified. Meta-analyses were carried out on maximal aerobic capacity, maximal voluntary contraction and body composition. Master endurance athletes (42.0 ± 6.6 ml kg^-1 min^-1) exhibited VO_2max values comparable with young healthy controls (43.1 ± 6.8 ml kg^-1 min^-1, P = .84), greater than older controls (27.1 ± 4.3 ml kg^-1 min^-1, P < 0.01) and master strength/power athletes (26.5 ± 2.3 mlkg^-1 min^-1, P < 0.01), and lower than young endurance trained individuals (60.0 ± 5.4 ml kg^-1 min^-1, P < 0.01). Master strength/power athletes (0.60 (0.28-0.93) P < 0.01) and young controls (0.71 (0.06-1.36) P < 0.05) were significantly stronger compared with the other groups. Body fat% was greater in master endurance athletes than young endurance trained (-4.44% (-8.44 to -0.43) P < 0.05) but lower compared with older controls (7.11% (5.70-8.52) P < 0.01).

CONCLUSION

Despite advancing age, this review suggests that chronic exercise training preserves physical function, muscular strength and body fat levels similar to that of young, healthy individuals in an exercise mode-specific manner.

Effects of 12 weeks of Nordic Walking and XCO Walking training on the endurance capacity of older adults

BACKGROUND

Several studies have already examined the positive effects of various forms of endurance training in patient groups and in healthy adults up to 60 years old. The aim of this study was to analyse the effects of Nordic Walking (NW) and XCO Walking (XCO) training on endurance capacity in healthy older adults, aged 60 years and older.

METHODS

Twenty-three older participants (mean age: 69.9 ± 5.4 years) were randomly assigned to either the NW group or the XCO group. All participants were measured before and after the 12 weeks of endurance training (2 sessions/week) to examine oxygen uptake (VO₂) and energy consumption during an outdoor field test. In addition, heart rates were recorded and lactate samples were collected.

RESULTS

NW mainly demonstrated some significant (p < 0.05) decreases in heart rate, lactate concentration at lower to moderate walking speeds, whereas XCO Walking revealed significant (p < 0.05) decreases in lactate concentration and VO₂ at low to higher walking speeds.

CONCLUSIONS

NW as well as XCO training increase the efficiency of the cardio-vascular system in older subjects. Both training approaches are suitable options for endurance training, which may serve to counteract age- and inactivity-related decreases in cardio-vascular functioning as well as aid in maintaining overall performance in older adults.

Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults

BACKGROUND

The ketogenic diet (KD) is a very low-carbohydrate, high-fat and adequate-protein diet that without limiting calories induces different metabolic adaptations, eg, increased levels of circulating ketone bodies and a shift to lipid metabolism. Our objective was to assess the impact of a 6-week non-energy-restricted KD in healthy adults beyond cohorts of athletes on physical performance, body composition, and blood parameters.

METHODS

Our single arm, before-and-after comparison study consisted of a 6-week KD with a previous preparation period including detailed instructions during classes and individual counselling by a dietitian. Compliance with the dietary regimen was monitored by measuring urinary ketones daily, and 7-day food records. All tests were performed after an overnight fast: cardiopulmonary exercise testing via cycle sprioergometry, blood samples, body composition, indirect calorimetry, handgrip strength, and questionnaires addressing complaints and physical sensations.

RESULTS

Forty-two subjects aged 37 ± 12 years with a BMI of 23.9 ± 3.1 kg/m² completed the study. Urinary ketosis was detectable on 97% of the days, revealing very good compliance with the KD. Mean energy intake during the study did not change from the habitual diet and 71.6, 20.9, and 7.7% of total energy intake were from fat, protein, and carbohydrates, respectively. Weight loss was -2.0 ± 1.9 kg (P < 0.001) with equal losses of fat-free and fat mass. VO₂peak and peak power decreased from 2.55 ± 0.68 l/min to 2.49 ± 0.69 l/min by 2.4% (P = 0.023) and from 241 ± 57 W to 231 ± 57 W by 4.1% (P < 0.001), respectively, whereas, handgrip strength rose slightly from 40.1 ± 8.8 to 41.0 ± 9.1 kg by 2.5% (P = 0.047). The blood lipids TG and HDL-C remained unchanged, whereas total cholesterol and LDL-C increased significantly by 4.7 and 10.7%, respectively. Glucose, insulin, and IGF-1 dropped significantly by 3.0, 22.2 and 20.2%, respectively.

CONCLUSIONS

We detected a mildly negative impact from this 6-week non-energy-restricted KD on physical performance (endurance capacity, peak power and faster exhaustion). Our findings lead us to assume that a KD does not impact physical fitness in a clinically relevant manner that would impair activities of daily living and aerobic training. However, a KD may be a matter of concern in competitive athletes.

TRIAL REGISTRATION

DRKS00009605, registered 08 January 2016.

Effects of caffeine ingestion on endurance performance in mentally fatigued individuals

PURPOSE

To examine the effects of caffeine ingestion on physiological and perceptual responses in mentally fatigued individuals.

METHODS

Eight male physically active subjects completed four cycling constant-workload tests in four experimental conditions at 80 % of maximal power output: control (C), mental fatigue (MF), mental fatigue plus caffeine ingestion (5 mg/kg) (MF-CAF), and mental fatigue plus placebo (MF-PLA). The mental fatigue was induced by a continuous performance task A-X version (AX-CPT). Before and after the AX-CPT, the profile of mood state (POMS) and blood samples for lactate measurement were collected. Oxygen consumption ([Formula: see text]), rating of perceived exertion (RPE), and electromyography (EMG) activity were measured during the cycling test.

RESULTS

The time to exhaustion in C, MF, MF-PLA, and MF-CAF were 251 ± 30, 222 ± 23, 248 ± 28, and 285 ± 42 s, respectively. Delta values (corrected by C condition) were higher in MF-CAF than MF (P = 0.031). MF-CAF reported higher Vigor scores when compared with C (P = 0.046) and MF (P = 0.020). RPE at the first minute was significantly higher in MF-PLA than in C (P = 0.050); at the second minute, RPE was higher in MF-PLA than in C (P = 0.049) and MF-CAF (P = 0.048). EMG activity was not different between the conditions.

CONCLUSIONS

Caffeine ingestion increased approximately 14 % endurance performance after the induction of mental fatigue. This effect was accompanied by a tendency to improvement in mood state (i.e., vigor). Therefore, caffeine ingestion can promote a beneficial effect on endurance performance in mentally fatigued individuals.

Conjugated linoleic acid (CLA) promotes endurance capacity via peroxisome proliferator-activated receptor δ-mediated mechanism in mice

Previously, it was reported that conjugated linoleic acid (CLA) with exercise training potentially improved endurance capacity via the peroxisome proliferator-activated receptor δ (PPARδ)-mediated mechanism in mice. This study determined the role of exercise and/or CLA in endurance capacity and PPARδ-associated regulators. Male 129Sv/J mice were fed either control (soybean oil) or CLA (0.5%) containing diets for 4 weeks and were further divided into sedentary or training regimes. CLA supplementation significantly reduced body weight and fat mass independent of exercise during the experimental period. Endurance capacity was significantly improved by CLA supplementation, while no effect of exercise was observed. Similarly, CLA treatment significantly increased expressions of sirtuin 1 and PPARγ coactivator-1α, up-stream regulators of PPARδ, in both sedentary and trained animals. With respect to downstream markers of PPARδ, CLA up-regulated the key biomarker needed to stimulate mitochondrial biogenesis, nuclear respiratory factor 1. Moreover, CLA supplementation significantly induced overall genes associated with muscle fibers, such as type I (slow-twitch) and type II (fast twitch). Taken together, it suggests that CLA improves endurance capacity independent of mild-intensity exercise via PPARδ-mediated mechanism.

Regulation of fuel metabolism during exercise in hypopituitarism with growth hormone-deficiency (GHD)

OBJECTIVE

Growth hormone (GH) has a strong lipolytic action and its secretion is increased during exercise. Data on fuel metabolism and its hormonal regulation during prolonged exercise in patients with growth hormone deficiency (GHD) is scarce. This study aimed at evaluating the hormonal and metabolic response during aerobic exercise in GHD patients.

DESIGN

Ten patients with confirmed GHD and 10 healthy control individuals (CI) matched for age, sex, BMI, and waist performed a spiroergometric test to determine exercise capacity (VO2max). Throughout a subsequent 120-minute exercise on an ergometer at 50% of individual VO2max free fatty acids (FFA), glucose, GH, cortisol, catecholamines and insulin were measured. Additionally substrate oxidation assessed by indirect calorimetry was determined at begin and end of exercise.

RESULTS

Exercise capacity was lower in GHD compared to CI (VO2max 35.5±7.4 vs 41.5±5.5ml/min∗kg, p=0.05). GH area under the curve (AUC-GH), peak-GH and peak-FFA were lower in GHD patients during exercise compared to CI (AUC-GH 100±93.2 vs 908.6±623.7ng∗min/ml, p<0.001; peak-GH 1.5±1.53 vs 12.57±9.36ng/ml, p<0.001, peak-FFA 1.01±0.43 vs 1.51±0.56mmol/l, p=0.036, respectively). There were no significant differences for insulin, cortisol, catecholamines and glucose. Fat oxidation at the end of exercise was higher in CI compared to GHD patients (295.7±73.9 vs 187.82±103.8kcal/h, p=0.025).

CONCLUSION

A reduced availability of FFA during a 2-hour aerobic exercise and a reduced fat oxidation at the end of exercise may contribute to the decreased exercise capacity in GHD patients. Catecholamines and cortisol do not compensate for the lack of the lipolytic action of GH in patients with GHD.

Lactose-free milk prolonged endurance capacity in lactose intolerant Asian males

Background

Several studies on Caucasian volunteers have proven that milk is an effective recovery drink for athletes. Such benefit, however, cannot be directly applied to the lactose-intolerant Asian population. This study investigated the effects of ingesting water (WT), sports drink (SPD) and lactose-free milk (LFM) on cycling capacity.

Methods

Ten healthy young men completed 3 randomized experimental trials. Each trial consisted of an intermittent glycogen depleting session, a 2 h recovery period during which they ingested the test drink, followed by cycling at 70% of their maximum oxygen consumption (VO₂max) to volitional exhaustion. Each trial was separated by at least one week.

Results

There were no complaints or symptoms of lactose intolerance during any of the trials. The cycling periods were different (p < 0.05) amongst the 3 trials, namely, lactose-free milk (LFM; 69.6 ± 14.0 min), sports drink (SPD; 52.1 ± 11.6 min), and water (WT; 36.0 ± 11.1 min), respectively. The VO₂ and VCO₂ of LFM (30 ± 4 and 29 ± 4 ml/kg/min) were lower (p < 0.05) than that of SPD (34 ± 4 and 34 ± 4 ml/kg/min) and WT (35 ± 4 and 33 ± 5 ml/kg/min). There were no differences (p = 0.45) in VO₂ and VCO₂ between SPD and WT. Mean rating of perceived exertion was lowest in LFM (14 ± 5; p < 0.05), while no difference was found between the other two trials (SPD: 16 ± 4 and WT: 16 ± 4; p = 0.18).

Conclusion

Lactose-free milk is likely to be an effective recovery drink for enhancing subsequent cycling capacity in lactose intolerant Asian males.

Heat acclimation decreases the growth hormone response to acute constant-load exercise in the heat

OBJECTIVE

The major objective of this study was to elucidate the effect of heat acclimation on blood growth hormone (GH) response to moderate intensity exhausting exercise in the heat. In addition, the potential relationship between inter-individual differences in GH response to exercise and variability in exercise-induced sweat loss was investigated.

DESIGN

Twenty young men completed three exercise tests on a treadmill: H1 (walk at 60% VO₂peak until exhaustion at 42 °C), N (walk at 22 °C; duration equal to H1) and H2 (walk until exhaustion at 42 °C after a 10-day heat acclimation program). Core temperature (T(c)) was recorded continuously and venous blood samples were taken before, during and after each exercise test. Exercise-induced sweat production was calculated on the basis of body mass change taking into account water intake and the volume of blood samples drawn.

RESULTS

Lower pre-exercise T(c), lower rate of rise in T(c) during exercise, and prolonged time to exhaustion in H2 compared with H1 revealed that the subjects successfully achieved an acclimated state. Overall, serum GH level was higher in H1 compared with both N and H2 (p<0.001) but did not differ between the two latter trials (p>0.05). T(c) correlated with serum GH concentration (r=0.615, p<0.01). Analysis of the individual data revealed a group (n=9) possessing a threshold-like pattern of the relationship between T(c) and blood GH response, whereas a plateau-like pattern was evident in the rest of the subjects (n=11). Both sweat production (r=0.596; p<0.001) and the rate of sweat production (r=0.457; p<0.001) correlated with the growth hormone area under the curve.

CONCLUSION

Heat acclimation decreases the GH response to moderate intensity exhausting exercise in the heat. GH may have a modest stimulating effect on whole-body sweat production during exercise.