Heat Stress Training Camps for Endurance Sport: A Descriptive Case Study of Successful Monitoring in 2 Ironman Triathletes

A common practice among endurance athletes is to purposefully train in hot environments during a "heat stress camp." However, combined exercise-heat stress poses threats to athlete well-being, and therefore, heat stress training has the potential to induce maladaptation. This case study describes the monitoring strategies used in a successful 3-week heat stress camp undertaken by 2 elite Ironman triathletes, namely resting heart rate variability, self-report well-being, and careful prescription of training based on previously collected physiological data. Despite the added heat stress, training volume very likely increased in both athletes, and training load very likely increased in one of the athletes, while resting heart rate variability and self-report well-being were maintained. There was also some evidence of favorable metabolic changes during routine laboratory testing following the camp. The authors therefore recommend that practitioners working with endurance athletes embarking on a heat stress training camp consider using the simple strategies employed in the present case study to reduce the risk of maladaptation and nonfunctional overreaching.

Incidence of V˙O2max Responders to Personalized versus Standardized Exercise Prescription

INTRODUCTION

Despite knowledge of cardiorespiratory fitness (CRF) training responders and nonresponders, it is not well understood how the exercise intensity prescription affects the incidence of response. The purpose of this study was to determine CRF training responsiveness based on cohort-specific technical error after 12 wk of standardized or individually prescribed exercise and the use of a verification protocol to confirm maximal oxygen uptake (V˙O2max).

METHODS

Sedentary adult participants (9 men, 30 women; 48.2 ± 12.2 yr) completed exercise training on 3 d·wk for 12 wk, with exercise intensity prescribed based on standardized methods using heart rate reserve or an individualized approach using ventilatory thresholds. A verification protocol was used at baseline and 12 wk to confirm the identification of a true V˙O2max and subsequent relative percent changes to quantify CRF training responsiveness. A cohort-specific technical error (4.7%) was used as a threshold to identify incidence of response.

RESULTS

Relative V˙O2max significantly increased (P < 0.05) from 24.3 ± 4.6 to 26.0 ± 4.2 and 29.2 ± 7.5 to 32.8 ± 8.6 mL·kg·min for the standardized and individualized groups, respectively. Absolute V˙O2max significantly increased (P < 0.05) from 2.0 ± 0.6 to 2.2 ± 0.6 and 2.4 ± 0.8 to 2.6 ± 0.9 L·min for the standardized and individualized groups, respectively. A significant difference in responsiveness was found between the individualized and standardized groups with 100% and 60% of participants categorized as responders, respectively.

CONCLUSIONS

A threshold model for exercise intensity prescription had a greater effect on the incidence of CRF training response compared with a standardized approach using heart rate reserve. The use of thresholds for intensity markers accounts for individual metabolic characteristics and should be considered as a viable and practical method to prescribe exercise intensity.

Exercise intensity regulates the effect of heat stress on substrate oxidation rates during exercise

Hyperthermia stimulates endogenous carbohydrate metabolism during exercise; however, it is not known if exercise intensity impacts the metabolic effect of heat stress. In the first study of this two-part investigation, endurance-trained male cyclists performed incremental exercise assessments in 18 and 35°C (60% rH). The stimulatory effect of heat stress on carbohydrate oxidation rates was greater at high vs. moderate vs. low relative intensity (P < 0.05). In agreement, no effects of heat stress on carbohydrate oxidation rates were observed during 60-min of subsequent low-intensity cycling. In study two, endurance-trained male cyclists performed 20-min of moderate-intensity (power at the first ventilatory threshold) and 5-min of high-intensity (power at the second ventilatory threshold) cycling in 18, 28, 34, and 40°C (60% rH). At moderate-intensity, carbohydrate oxidation rates were significantly elevated by heat stress in 40°C (P < 0.05), whereas at high-intensity carbohydrate oxidation rates were significantly elevated by heat stress in 34 and 40°C (P < 0.05). This exercise intensity-mediated regulation of the effect of heat stress on carbohydrate oxidation may be partially attributable to observed plasma adrenaline responses. Our data suggest that under moderate environmental heat stress (34-35°C, 60% rH), heat stress-induced changes in CHO oxidation rates are unlikely to occur unless the relative exercise intensity is high (81 ± 8%⩒O_2max), whereas under more extreme environmental heat stress (40°C, 60% rH), these changes occur at lower relative intensities (69 ± 8%⩒O_2max). This provides indication of when heat stress-induced metabolic changes during exercise are likely to occur.

Activity Profile of Elite Netball Umpires During Match Play

Spencer, KN, Paget, N, Farley, ORL, and Kilding, AE. Activity profile of elite netball umpires during match play. J Strength Cond Res 34(10): 2832-2839, 2020-The study aimed to determine activity profiles of officials in elite netball. Physical demands of Load·min (au) representing accumulated accelerations by triaxial accelerometers during matches and exercise-to-rest ratio were measured using global positioning systems (Catapult, MinimaxX S4). Physiological demands were quantified by estimated equivalent distance and heart rate (HR) (MeanHR, percentage HRpeak, and HRzones) and movement variables (frequency, mean time, and percentage of total time) were coded using Sportscode Elite (Version 10, Hudl, Lincoln, Nebraska). Differences were analyzed by periods (Q1-Q4). Load·min (au) (M = 407 ± 66) significantly varied with time (F [3, 55] = 3.42, p = 0.02) and the highest percentage of exercise-to-rest performed in Q1 (21 ± 5%). Estimated equivalent distance (3,839 ± 614 m) varied significantly with time (F [3, 56] = 3.18, p = 0.03), the umpires spent longest duration of time (35%) in HRzone 3 (75-85% of HRpeak). Mean HR significantly decreased with time (p < 0.01; Q1 [157 ± 13], quarter 2 [156 ± 12], and Q4 [153 ± 14]). Umpires spent 77% in rest-recovery ratio movements and 23% of time exercise-to-rest ratio. In summary, netball umpiring is characterized by intermittent, short, high-intensity activity (sprinting, sidestepping, and turn to change direction), with increasing periods of rest-recovery (walking and standing).

Time Course Changes in Confirmed 'True' VO 2 max After Individualized and Standardized Training

This study sought to examine time course changes in maximal oxygen consumption (VO ₂ max) confirmed with verification testing following 12 weeks of standardized vs. individualized exercise training. Participants (N=39) were randomly allocated to differing exercise intensity prescription groups: ventilatory threshold (individualized) or % heart rate reserve (standardized). At baseline, 4, 8, and 12 weeks, participants completed maximal exercise testing with a verification protocol to confirm ‘true VO ₂ max.’ VO ₂ max in the standardized group changed from 24.3±4.6 ml·kg ⁻¹ ·min ⁻¹ at baseline to 24.7±4.6, 25.9±4.7, and 26.0±4.2 ml·kg ⁻¹ ·min ⁻¹ at week 4, 8, and 12, respectively, with a significant difference (p<0.05) in VO ₂ max at week 8 and 12 compared to baseline. The individualized group had increases in VO ₂ max from _{online 2} 9.5±7.5 ml·kg ⁻¹ ·min ⁻¹ at baseline to 30.6±8.4, 31.4±8.4, and 32.8±8.6 ml·kg ⁻¹ ·min ⁻¹ at week 4, 8, and 12, respectively. In the individualized group, there were significant differences (p<0.05) in VO ₂ max from baseline to week 8 and 12 and a significant increase in VO ₂ max from week 8 to 1 _{online 2} . Although not statistically significant, our preliminary data demonstrates a more rapid and potent improvement in VO ₂ max when exercise intensity is individualized. This is the first investigation to employ use of the verification procedure to confirm ‘true VO ₂ max’ changes following exercise training using ventilatory thresholds.

Keeping Athletes Healthy at the 2020 Tokyo Summer Games: Considerations and Illness Prevention Strategies

Keeping athletes healthy will be important for optimal athletic performance at the 2020 Tokyo Summer Olympic and Paralympic Games. Athletes will be exposed to several stressors during the preparatory and competition phases of the Summer Games that have the potential to depress immunity and increase illness risk. This mini-review provides an overview on effective and practical stressor-specific illness prevention strategies that can be implemented to maintain and protect the health of Olympic and Paralympic athletes.

Effects of upper and lower body wearable resistance on spatio-temporal and kinetic parameters during running

Wearable resistance training involves added load attached directly to the body during sporting movements. The effects of load position during running are not yet fully established. Therefore, the purpose of this research was to determine spatio-temporal and kinetic characteristics during submaximal running using upper, lower and whole-body wearable resistance (1-10% body mass (BM)). Twelve trained male runners completed eight 2-min treadmill running bouts at 3.9 m/s with and without wearable resistance. The first and last bouts were unloaded, while the middle 6 were randomised wearable resistance conditions: upper body (UB) 5% BM, lower body (LB) 1%, 3%, 5% BM and whole body (WB) 5%, 10% BM. Wearable resistance of 1-10% BM resulted in a significant increase in heart rate (5.40-8.84%), but minimal impact on spatio-temporal variables. Loads of 5% BM and greater caused changes in vertical stiffness, vertical and horizontal force, and impulse. Functional and effective propulsive force (2.95%, 2.88%) and impulse (3.40%, 3.38%) were significantly (p < 0.05) greater with LB5% than UB5%. Wearable resistance may be used to increase muscular kinetics during running without negatively impacting spatio-temporal variables. The application of these findings will vary depending on athlete goals. Future longitudinal studies are required to validate training contentions.

From Lab to Real World: Heat Acclimation Considerations for Elite Athletes

As major sporting events are often held in hot environments, increased interest in ways of optimally heat acclimating athletes to maximise performance has emerged. Heat acclimation involves repeated exercise sessions in hot conditions that induce physiological and thermoregulatory adaptations that attenuate heat-induced performance impairments. Current evidence-based guidelines for heat acclimation are clear, but the application of these recommendations is not always aligned with the time commitments and training priorities of elite athletes. Alternative forms of heat acclimation investigated include hot water immersion and sauna bathing, yet uncertainty remains around the efficacy of these methods for reducing heat-induced performance impairments, as well as how this form of heat stress may add to an athlete's overall training load. An understanding of how to optimally prescribe and periodise heat acclimation based on the performance determinants of a given event is limited, as is knowledge of how heat acclimation may affect the quality of concurrent training sessions. Finally, differences in individual athlete responses to heat acclimation need to be considered. This article addresses alternative methods of heat acclimation and heat exposure, explores gaps in literature around understanding the real world application of heat acclimation for athletes, and highlights specific athlete considerations for practitioners.

Contextualising Maximal Fat Oxidation During Exercise: Determinants and Normative Values

Using a short-duration step protocol and continuous indirect calorimetry, whole-body rates of fat and carbohydrate oxidation can be estimated across a range of exercise workloads, along with the individual maximal rate of fat oxidation (MFO) and the exercise intensity at which MFO occurs (Fatmax). These variables appear to have implications both in sport and health contexts. After discussion of the key determinants of MFO and Fatmax that must be considered during laboratory measurement, the present review sought to synthesize existing data in order to contextualize individually measured fat oxidation values. Data collected in homogenous cohorts on cycle ergometers after an overnight fast was synthesized to produce normative values in given subject populations. These normative values might be used to contextualize individual measurements and define research cohorts according their capacity for fat oxidation during exercise. Pertinent directions for future research were identified.

Using a site-specific technical error to establish training responsiveness: a preliminary explorative study

BACKGROUND

Even though cardiorespiratory fitness (CRF) training elicits numerous health benefits, not all individuals have positive training responses following a structured CRF intervention. It has been suggested that the technical error (TE), a combination of biological variability and measurement error, should be used to establish specific training responsiveness criteria to gain further insight on the effectiveness of the training program. To date, most training interventions use an absolute change or a TE from previous findings, which do not take into consideration the training site and equipment used to establish training outcomes or the specific cohort being evaluated. The purpose of this investigation was to retrospectively analyze training responsiveness of two CRF training interventions using two common criteria and a site-specific TE.

METHODS

Sixteen men and women completed two maximal graded exercise tests and verification bouts to identify maximal oxygen consumption (VO2max) and establish a site-specific TE. The TE was then used to retrospectively analyze training responsiveness in comparison to commonly used criteria: percent change of >0% and >+5.6% in VO2max.

RESULTS

The TE was found to be 7.7% for relative VO2 max. χ2 testing showed significant differences in all training criteria for each intervention and pooled data from both interventions, except between %Δ >0 and %Δ >+7.7% in one of the investigations. Training nonresponsiveness ranged from 11.5% to 34.6%.

CONCLUSION

Findings from the present study support the utility of site-specific TE criterion to quantify training responsiveness. A similar methodology of establishing a site-specific and even cohort specific TE should be considered to establish when true cardiorespiratory training adaptations occur.

Acute effects of heated resistance exercise in female and male power athletes

PURPOSE

To determine the effects of heated resistance exercise on thermal strain, neuromuscular function and hormonal responses in power athletes.

METHODS

Sixteen (n = 8 female; 8 male) highly trained power athletes completed a combined strength and power resistance exercise session in hot (HOT ~30 °C) and temperate (CON ~20 °C) conditions. Human growth hormone (hGH), cortisol and testosterone concentrations in plasma, peak power (counter-movement jump, CMJ) and peak force (isometric mid-thigh pull) were measured before and after each training session; thermoregulatory responses were monitored during training.

RESULTS

Skin temperature, thermal sensation and thermal discomfort were higher in HOT compared with CON. Sweat rate was higher in HOT for males only. Compared with CON, HOT had trivial effects on core temperature and heart rate. During HOT, there was a possible increase in upper-body power (medicine ball throw) in females [3.4% (90% CL -1.5, 8.6)] and males [(3.3% (-0.1, 6.9)], while lower-body power (vertical jump) was enhanced in males only [3.2% (-0.4, 6.9)]. Following HOT, CMJ peak power [4.4% (2.5; 6.3)] and strength [8.2% (3.1, 13.6)] were enhanced in female athletes, compared with CON, while effects in males were unclear. Plasma hGH concentration increased in females [83% (18; 183)] and males [107% (-21; 444)] in HOT compared with CON, whereas differential changes occurred for cortisol and testosterone.

CONCLUSION

Heated resistance exercise enhanced power and increased plasma hGH concentration in female and males power athletes. Further research is required to assess the ergogenic potential of resistance exercise in the heat.

Effects of Acutely Intermittent Hypoxic Exposure on Running Economy and Physical Performance in Basketball Players

Kilding, AE, Dobson, BP, and Ikeda, E. Effects of acutely intermittent hypoxic exposure on running economy and physical performance in basketball players. J Strength Cond Res 30(7): 2033-2042, 2016-The aim of this study was to determine the effect of short duration intermittent hypoxic exposure (IHE) on physical performance in basketball players. Using a single-blind placebo-controlled group design, 14 trained basketball players were subjected to 15 days of passive short duration IHE (n = 7), or normoxic control (CON, n = 7), using a biofeedback nitrogen dilution device. A range of physiological, performance, and hematological variables were measured at baseline, and 10 days after IHE. After intervention, the IHE group, relative to the CON group, exhibited improvements in the Yo-Yo intermittent recovery level 1 (+4.8 ± 1.6%; effect size [ES]: 1.0 ± 0.4) and repeated high-intensity exercise test performance (-3.5 ± 1.6%; ES: -0.4 ± 0.2). Changes in hematological parameters were minimal, although soluble transferrin receptor increased after IHE (+9.2 ± 10.1%; ES: 0.3 ± 0.3). Running economy at 11 km·h (-9.0 ± 9.7%; ES: -0.7 ± 0.7) and 13 km·h was improved (-8.2 ± 6.9%; ES: -0.7 ± 0.5), but changes to V[Combining Dot Above]O2peak, HRpeak, and lactate were unclear. In summary, acutely IHE resulted in worthwhile changes in physical performance tests among competitive basketball players. However, physiological measures explaining the performance enhancement were in most part unclear.

The incidence of training responsiveness to cardiorespiratory fitness and cardiometabolic measurements following individualized and standardized exercise prescription: study protocol for a randomized controlled trial

BACKGROUND

There is individual variability to cardiorespiratory fitness (CRF) training, but the underlying cause is not well understood. Traditionally, a standardized approach to exercise prescription has utilized relative percentages of maximal heart rate, heart rate reserve (HRR), maximal oxygen uptake (VO2max), or VO2 reserve to establish exercise intensity. However, this model fails to take into consideration individual metabolic responses to exercise and may attribute to the variability in training responses. It has been proposed that an individualized approach would take into consideration metabolic responses to exercises to increase responsiveness to training.

METHODS

In this randomized control trial, participants will undergo a 12-week exercise intervention using individualized (ventilatory thresholds) and standardized (HRR) methods to prescribe CRF training intensity. Following the intervention, participants will be categorized as responders or non-responders based on changes in maximal aerobic abilities. Participants who are non-responders will complete a second 12-week intervention in a crossover design to determine whether they can become responders with a differing exercise prescription. There are four main research outcomes: (1) determine the cohort-specific technical error to use in the categorization of response rate; (2) determine if an individualized intensity prescription is superior to a standard approach in regards to VO2max and cardiometabolic risk factors; (3) investigate the time course changes throughout 12 weeks of CRF training between the two intervention groups; and (4) determine if non-responders can become responders if the exercise prescription is modified.

DISCUSSION

The findings from this research will provide evidence on the effectiveness of individualized exercise prescription related to training responsiveness of VO2max and cardiometabolic risk factors compared to a standardized approach and further our understanding of individual exercise responses. If the individualized approach proposed is deemed effective, it may change the way exercise specialists prescribe exercise intensity to enhance training responsiveness.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02868710 . Registered on 15 August 2016.

Periodizing heat acclimation in elite Laser sailors preparing for a world championship event in hot conditions

Purpose: To examine the retention and re-acclimation responses during a periodized heat acclimation (HA) protocol in elite sailors preparing for the 2013 World Championships in Muscat, Oman (∼27–30°C, 40–60% RH). Methods: Two elite male Laser class sailors completed 5 consecutive days of HA (60 min per day in 35°C, 60% RH). Heat response tests (HRT) were performed on day 1 and 5 of HA, then 1 (decay 1, D1) and 2 (D2) weeks following HA. Participants were then re-acclimated (RA) for 2 days, within the next week, before a final HRT ∼72 h post-RA. Rectal temperature, plasma volume, heart rate, sweat rate, as well as thermal discomfort and rating of perceived exertion were measured during each HRT. Results: Rectal temperature decreased with HA (0.46 ± 0.05°C), while individual responses following D1, D2 and RA varied. Heart rate (14 ± 7 bpm), thermal discomfort (0.6 ± 0.1 AU) and rating of perceived exertion (1.8 ± 0.6 AU) decreased across HA, and adaptations were retained by D2. Plasma volume steadily increased over the decay period (D2 = 8.0 ± 1.3%) and after RA (15.5 ± 1.1%) compared with baseline. RA resulted in further thermoregulatory improvements in each Athlete, although individual adjustments varied. Conclusion: Heat strain was reduced in elite Laser sailors following HA and most thermoregulatory adaptations were retained for 2 weeks afterwards. RA may ‘top up’ adaptations after 2 weeks of HA decay.

Strategies to improve running economy

Running economy (RE) represents a complex interplay of physiological and biomechanical factors that is typically defined as the energy demand for a given velocity of submaximal running and expressed as the submaximal oxygen uptake (VO2) at a given running velocity. This review considered a wide range of acute and chronic interventions that have been investigated with respect to improving economy by augmenting one or more components of the metabolic, cardiorespiratory, biomechanical or neuromuscular systems. Improvements in RE have traditionally been achieved through endurance training. Endurance training in runners leads to a wide range of physiological responses, and it is very likely that these characteristics of running training will influence RE. Training history and training volume have been suggested to be important factors in improving RE, while uphill and level-ground high-intensity interval training represent frequently prescribed forms of training that may elicit further enhancements in economy. More recently, research has demonstrated short-term resistance and plyometric training has resulted in enhanced RE. This improvement in RE has been hypothesized to be a result of enhanced neuromuscular characteristics. Altitude acclimatization results in both central and peripheral adaptations that improve oxygen delivery and utilization, mechanisms that potentially could improve RE. Other strategies, such as stretching should not be discounted as a training modality in order to prevent injuries; however, it appears that there is an optimal degree of flexibility and stiffness required to maximize RE. Several nutritional interventions have also received attention for their effects on reducing oxygen demand during exercise, most notably dietary nitrates and caffeine. It is clear that a range of training and passive interventions may improve RE, and researchers should concentrate their investigative efforts on more fully understanding the types and mechanisms that affect RE and the practicality and extent to which RE can be improved outside the laboratory.

ACE and UCP2 gene polymorphisms and their association with baseline and exercise-related changes in the functional performance of older adults

Maintaining high levels of physical function is an important aspect of successful ageing. While muscle mass and strength contribute to functional performance in older adults, little is known about the possible genetic basis for the heterogeneity of physical function in older adults and in how older adults respond to exercise. Two genes that have possible roles in determining levels of muscle mass, strength and function in young and older adults are angiotensin-converting enzyme (ACE) and mitochondrial uncoupling protein 2 (UCP2). This study examined whether polymorphisms in these two individual genes were associated with baseline functional performance levels and/or the training-related changes following exercise in previously untrained older adults. Five-eight Caucasian older adults (mean age 69.8 years) with no recent history of resistance training enrolled in a 12 week program of resistance, balance and cardiovascular exercises aimed at improving functional performance. Performance in 6 functional tasks was recorded at baseline and after 12 weeks. Genomic DNA was assayed for the ACE intron 16 insertion/deletion (I/D) and the UCP2 G-866A polymorphism. Baseline differences among genotype groups were tested using analysis of variance. Genotype differences in absolute and relative changes in physical function among the exercisers were tested using a general linear model, adjusting for age and gender. The genotype frequencies for each of the studied polymorphisms conformed to the Hardy-Weinberg equilibrium. The ACE I/D genotype was significantly associated with mean baseline measures of handgrip strength (II 30.9 ± 3.01 v. ID 31.7 ± 1.48 v. DD 29.3 ± 2.18 kg, p < 0.001), 8ft Up and Go time (II 6.45 ± 0.48 v. ID/DD 4.41 ± 0.19 s, p < 0.001) and 6 min walk distance (II 458 ± 28.7 v. ID/DD 546 ± 12.1m, p = 0.008). The UCP2 G-866A genotype was also associated with baseline 8ft Up and Go time (GG 5.45 ± 0.35 v. GA 4.47 ± 0.26 v. AA 3.89 ± 0.71 s, p = 0.045). After 12 weeks of training, a significant difference between UCP2 G-886A genotype groups for change in 8ft Up and Go time was detected (GG −0.68 ± 0.17 v. GA −0.10 ± 0.14 v. AA +0.05 ± 0.31 s, p = 0.023). While several interesting and possibly consistent associations with older adults’ baseline functional performance were found for the ACE and UCP2 polymorphisms, we found no strong evidence of genetic associations with exercise responses in this study. The relative equivalence of some of these training-response findings to the literature may have reflected the current study’s focus on physical function rather than just strength, the relatively high levels of baseline function for some genotype groups as well as the greater statistical power for detecting baseline differences than the training-related changes.

Lower-body determinants of running economy in male and female distance runners

A variety of training approaches have been shown to improve running economy in well-trained athletes. However, there is a paucity of data exploring lower-body determinants that may affect running economy and account for differences that may exist between genders. Sixty-three male and female distance runners were assessed in the laboratory for a range of metabolic, biomechanical, and neuromuscular measures potentially related to running economy (ml·kg(-1)·min(-1)) at a range of running speeds. At all common test velocities, women were more economical than men (effect size [ES] = 0.40); however, when compared in terms of relative intensity, men had better running economy (ES = 2.41). Leg stiffness (r = -0.80) and moment arm length (r = 0.90) were large-extremely largely correlated with running economy and each other (r = -0.82). Correlations between running economy and kinetic measures (peak force, peak power, and time to peak force) for both genders were unclear. The relationship in stride rate (r = -0.27 to -0.31) was in the opposite direction to that of stride length (r = 0.32-0.49), and the relationship in contact time (r = -0.21 to -0.54) was opposite of that of flight time (r = 0.06-0.74). Although both leg stiffness and moment arm length are highly related to running economy, it seems that no single lower-body measure can completely explain differences in running economy between individuals or genders. Running economy is therefore likely determined from the sum of influences from multiple lower-body attributes.