The effect of discretionary snack consumption on overall energy intake, weight status, and diet quality: A systematic review.

The consumption frequency and portion size of discretionary snacks are thought to contribute to a greater food intake and risk of overweight or obesity in the developed world but evidence from epidemiological studies is inconclusive. To investigate this, we systematically evaluated evidence on the effects of discretionary snack consumption on weight status, energy intake, and diet quality. Articles involving discretionary snacks reported against the outcome measures of any primary, peer-reviewed study using human participants from free-living conditions for all age groups were included. A total of 14,780 titles were identified and 40 eligible publications were identified. Three key outcomes were reported: weight status (n = 35), energy intake (n = 11), and diet quality (n = 3). Increased discretionary snack consumption may contribute modestly to energy intake, however, there is a lack of consistent associations with increased weight/BMI. Although cross-sectional analyses offered conflicting findings, longitudinal studies in adults showed a consistent positive relationship between discretionary snack intake and increasing weight or body mass index. Given that experimental findings suggest reducing the size of discretionary snacks could lead to decreased consumption and subsequent energy intake, food policy makers and manufacturers may find it valuable to consider altering the portion and/or packaging size of discretionary snacks.

The Efficacy of a Multimodal Recovery Strategy Implemented After a High-Intensity Rugby League Training Session.

ABSTRACT: Aben, HGJ, Hills, SP, Higgins, D, Cooke, CB, Davis, D, Jones, B, and Russell, M. The efficacy of a multimodal recovery strategy implemented after a high-intensity rugby league training session. J Strength Cond Res 37(8): 1634-1642, 2023-The efficacy of a multimodal recovery strategy implemented within 4 hours of rugby league (RL) training was investigated using repeated-measures, randomized, crossover methods in 10 professional academy RL players (age: 17 ± 1 years). Following standardized training (5,383 m covered, 350-m high-speed running, 28 repeated high-intensity efforts, 24 collisions), players completed a multimodal recovery (REC) strategy (i.e., ∼640 kcal meal + ∼1,285 kcal snacks or drinks, cold-water immersion, sleep hygiene recommendations) or control (i.e., ∼640 kcal meal: CONT) practices. Isometric mid-thigh pulls (IMTP), countermovement jumps (CMJ), and wellness questionnaires were completed before (-3 hours) and after (+24, +48 hours) training. The recovery strategy influenced IMTP peak force ( p = 0.026), but between-trial differences were undetectable. No other between-trial effects (all p > 0.05) were seen for IMTP, CMJ, or wellness variables. Training-induced reductions in CMJ peak power (-4 ± 6% vs baseline: 4,878 ± 642 W) at +24 hours ( p = 0.016) dissipated by +48 hours. Fatigue and lower-body soreness reduced by 16 ± 19% ( p = 0.01) and 32 ± 44% ( p = 0.024) at +48 hours versus +24 hours, respectively. Relative to CONT (i.e., posttraining nutrition), the effects of a single bout of recovery practices appeared limited when implemented after RL-specific training. Therefore, when training included limited collisions, balanced postexercise meals appeared equally effective relative to a multimodal recovery strategy. Transient changes in performance and wellness variables after training may have implications for practitioners. Consecutive training sessions, including a high frequency and intensity of eccentric muscle actions, should be carefully planned, especially near match-play.

Profiling the Post-match Recovery Response in Male Rugby: A Systematic Review.

ABSTRACT: Aben, HGJ, Hills, SP, Cooke, CB, Davis, D, Jones, B, and Russell, M. Profiling the post-match recovery response in male rugby: A systematic review. J Strength Cond Res 36(7): 2050-2067, 2022-To minimize underperformance, injury, and illness, and to enhance readiness for training and match-play, post-match responses are commonly monitored within professional rugby. As no clear consensus exists regarding the magnitude and duration of post-match recovery, this review summarized the literature (17 studies yielded from literature searching/screening) reporting neuromuscular (countermovement jump [CMJ], peak power output [PP], and flight time [FT]), biochemical (creatine kinase [CK]) or endocrine (cortisol [C] and testosterone [T] concentrations), and subjective (wellness questionnaire and muscle soreness) indices after rugby match-play. For neuromuscular responses (11 studies), reductions in PP <31.5% occurred <30 minutes after match, returning to baseline within 48-72 hours. Post-match reductions in FT of <4% recovered after 48 hours. For biochemical and endocrine responses (14 studies), increases in CK, ranging from 120 to 451%, peaked between 12 and 24 hours, returning to baseline within 72 hours of match-play. Initial increases of <298% in C and reductions in T concentrations (<44%) returned to pre-match values within 48-72 hours. Mood disturbances (6 studies) required 48-72 hours to normalize after peak decrements of <65% at 24 hours. This review highlights that 72 hours were needed to restore perturbations in neuromuscular, biochemical and endocrine, and subjective/perceptual responses after competitive rugby match-play. Notably, only 4 studies reported responses in more ecologically valid scenarios (i.e., those in which regular training and recovery strategies were used) while also reporting detailed match demands. A lack of research focusing on youth players was also evident, as only 3 studies profiled post-match responses in younger athletes. Deeper insight regarding post-match responses in ecologically valid scenarios is therefore required.

Quantifying the Peak Physical Match-Play Demands of Professional Soccer Substitutes Following Pitch-Entry: Assessing Contextual Influences.

Purpose: To quantify the peak post-pitch-entry physical responses of soccer substitutes while assessing contextual influences. Peak responses may be important performance indicators for substitutes introduced to provide a physical impact. Method: Thirty-three professional substitutes wore Microelectromechanical Systems during 44 matches (4 ± 3 observations·player-1). Post-pitch-entry relative peak values for total and high-speed (> 5.5 m·s-1) distances, average acceleration, and PlayerLoad™ were calculated using rolling averages over 60-s to 600-s. Linear mixed models assessed contextual influences (position, substitution timing, scoreline, and location). Results: Substitutes introduced during the final ~15 min of match-play covered less high-speed distance than first-half substitutes (~2.8-3.1 m·min-1) over 480-s to 600-s epochs, and less than 60:00-74:59 min substitutes (~1.7-1.8 m·min-1) during 540-s and 600-s epochs. Average acceleration during all except 180-s epochs was lower for 75:00+ min substitutes compared with first-half replacements (~0.27-0.43 m·s-2), and lower than 60:00-74:59 min substitutes during 60-s (~0.13 m·s-2). Substitutes introduced when their team was winning recorded greater distances over 120-s to 600-s (~6.2-7.7 m·min-1), and higher PlayerLoad™ values during 120-s, 180-s, 300-s, and 480-s epochs (~2.7-3.6 arbitrary units·min-1), compared with when scores were level at pitch-entry. Irrespective of substitution timing, substitute midfielders exceeded the total distance of substitute attackers (~5.9-16.2 m·min-1) for all except 360-s and 600-s epochs, and defenders (~13.3-26.7 m·min-1) during epochs < 300-s. Conclusions: This study provides benchmark data for practitioners tailoring training and recovery protocols, particularly "top-up" conditioning, to the competitive demands of soccer substitutes. Knowing how contextual factors influence substitutes' peak match-play responses may help managers/coaches assess the efficacy of substitution strategies.

Development and Maintenance of Sprint Training Adaptations: An Uphill-Downhill Study.

ABSTRACT: Bissas, A, Paradisis, GP, Nicholson, G, Walker, J, Hanley, B, Havenetidis, K, and Cooke, CB. Development and maintenance of sprint training adaptations: an uphill-downhill study. J Strength Cond Res 36(1): 90-98, 2022-We examined the development of performance adaptations resulting from an uphill-downhill training program and monitored the decline of adaptations during detraining. Twenty-eight men were randomly assigned to 1 of 2 sprint training groups who trained 3 times per week for 6 weeks and a control group (C). The uphill-downhill group (U+D) trained on an 80-m platform with 3° slopes, whereas the horizontal (H) group trained on flat track. Subjects were tested for maximal running speed (MRS), associated kinematics, and leg strength before and after training, with U+D subjects also tested after weeks 2 and 4 of training, and after a 3-week detraining period. The U+D group increased their MRS by 3.7% (from 8.75 ± 0.72 to 9.07 ± 0.64 m·s-1, p < 0.05), their stride rate by 3.1% (from 4.21 ± 0.21 to 4.34 ± 0.18 Hz, p < 0.05), and their knee extensors' maximum isometric force by 21% (from 2,242 ± 489 to 2,712 ± 498 N, p < 0.05) after training. The time course of changes showed declines for weeks 1-4 (1.4-5.1%), but an ascending trend of improvement compensated all losses by the end of week 6 (p < 0.05). During detraining, no decreases occurred. No changes were observed for the H and C groups. The minimum period to produce positive effects was 6 weeks, with a very good standard of performance maintained 3 weeks after training. U+D training will prove useful for all athletes requiring fast adaptations, and it can fit into training mesocycles because of its low time demands.

Body temperature and physical performance responses are not maintained at the time of pitch-entry when typical substitute-specific match-day practices are adopted before simulated soccer match-play.

OBJECTIVES: To profile performance and physiological responses to typical patterns of match-day activity for second-half soccer substitutes. DESIGN: Descriptive. METHODS: Following a warm-up, 13 male team sports players underwent ∼85min of rest, punctuated with five min rewarm-ups at ∼25, ∼50, and ∼70min, before ∼30min of simulated soccer match-play. Countermovement jump performance (jump height, peak power output), alongside 15m sprints, were assessed post-warm-up, and pre- and post-simulated match-play. Core temperature, heart rate, ratings of perceived exertion, and blood glucose and lactate concentrations were measured throughout. RESULTS: Warm-up-induced core temperature elevations (∼2.3%, +0.85°C; p<0.001) were maintained until after the first rewarm-up. Thereafter, core temperature was reduced from post-warm-up values until pre-simulated match-play (∼1.6%, -0.60°C; p<0.001), where values were similar to pre-warm-up (37.07±0.24°C, p=0.981). Simulated match-play increased core temperature progressively (p≤0.05) but values remained lower than post-warm-up (∼5min; p=0.002) until ∼10min into exercise. From post-warm-up to pre-simulated match-play, sprint times (∼3.9%, +0.10s, p=0.003), jump height (∼9.4%, -3.1cm; p=0.017), and peak power output (∼7.2%, -296W; p<0.001) worsened. Despite increased ratings of perceived exertion and elevated blood lactate concentrations (p≤0.05), sprint times were maintained throughout exercise, whereas peak power increased (∼7.8%, +294W; p=0.006) pre- to post-exercise. CONCLUSIONS: At the point of simulated pitch-entry, body temperature and physical performance responses were not maintained from warm-up cessation despite typical substitute-specific match-day practices being employed in thermoneutral conditions. Evidence of performance-limiting fatigue was absent during ∼30min of simulated match-play. These data question the efficacy of practices typically implemented by substitutes before pitch-entry.

Profiling the Post-match Top-up Conditioning Practices of Professional Soccer Substitutes: An Analysis of Contextual Influences.

Hills, SP, Barrett, S, Busby, M, Kilduff, LP, Barwood, MJ, Radcliffe, JN, Cooke, CB, and Russell, M. Profiling the post-match top-up conditioning practices of professional soccer substitutes: An analysis of contextual influences. J Strength Cond Res 34(10): 2805-2814, 2020-Soccer practitioners implement "top-up" conditioning sessions to compensate for substitutes' limited match-play exposure. Although perceived to be valuable for reducing injury risk and augmenting positive physical adaptations, little research has considered the demands of post-match top-up training. To quantify post-match top-up responses, 31 professional soccer players wore 10 Hz microelectromechanical systems after 37 matches whereby they were selected in the match-day squad as substitutes (184 observations; 6 ± 5 observations·player). Linear mixed models and effect sizes (ES) assessed the influence of contextual factors on 23 physical performance variables. Top-ups lasted 17.13 ± 7.44 minutes, eliciting total and high-speed distances of 1.7 ± 6.2 km and 0.4 ± 1.7 km, respectively. Each contextual factor (i.e., position, substitution timing, match location, result, time of day, stage of the season, and fixture density) influenced at least 4 of the dependent variables profiled (p ≤ 0.05). Top-up duration; total, moderate-speed, and low-speed distance; and the number of repeated high-intensity efforts were greater for unused vs. used substitutes (ES: 0.38-0.73, small to moderate). Relative to away matches, home top-ups elicited heightened total, low-speed, and high-speed distances, alongside more moderate-speed accelerations and decelerations, and repeated high-intensity efforts (ES: 0.25-0.89, small to moderate). Although absolute and relative running distances were generally the highest when the fixture density was low, the greatest acceleration and deceleration demands were observed during the most congested fixture periods. Late-season top-ups typically elicited lower absolute physical responses than early and mid-season sessions. These data provide important information for practitioners when considering the aims and design of substitute top-up conditioning sessions, particularly with reference to contextual influences.

Modifying the pre-pitch entry practices of professional soccer substitutes may contribute towards improved movement-related performance indicators on match-day: A case study.

Modifying a soccer substitute's pre-pitch-entry activities may represent an opportunity to maximise physical performance and minimise injury-risk following match-introduction. Using a professional team that has previously participated in substitute profiling research, this follow-up case study investigated the effects of a modified match-day protocol that included substitutes; 1) performing a new pre-match warm-up alongside members of the starting team (as opposed to a separate substitute-only warm-up), 2) participating in a staff-led half-time rewarm-up (as opposed to player-led half-time activities), and 3) receiving ongoing education focusing on the efficacy of (re)warm-up activities. English Championship substitutes (n = 15) were monitored using Micro-electromechanical Systems during 13 matches incorporating the modified practices (35 observations). On an individual player basis, data were organised into bouts of warm-up activity (pre-pitch-entry) and five min epochs of match-play (post-pitch-entry). Linear mixed modelling assessed the influence of 'bout' and 'epoch', position, and scoreline. Substitutes performed 3±1 rewarm-up bouts∙player-1∙match-1 between kick-off and pitch-entry, which were shorter (-17.2 to -27.1 min) and elicited less distance (-696 to -1257 m) than the pre-match warm-up (p≤0.001). Compared with previous data, heightened absolute movement responses were observed during the pre-match and staff-led half-time (re)warm-ups, alongside greater relative distances covered during player-led activities performed between kick-off and pitch-entry. Whilst less distance (-10%) was covered during the second versus first five min period following match-introduction, values remained higher than previously reported. Between pitch-entry and the end of the match, the scoreline improved and worsened following 26% and 11% of substitutions, respectively; a favourable record compared with existing observations. Acknowledging the likely contribution from external factors, this case study reports heightened movement profiles and improved match scorelines when pre-pitch-entry practices were modified. Practitioners should note the potential influence of match-day activities on the physical responses of soccer substitutes and, if deemed necessary, consider adapting their pre-pitch-entry routines accordingly.

The Reliability of Neuromuscular and Perceptual Measures Used to Profile Recovery, and the Time-Course of such Responses following Academy Rugby League Match-Play.

In professional academy rugby league (RL) players, this two-part study examined; A) the within- and between-day reliability of isometric mid-thigh pulls (IMTP), countermovement jumps (CMJ), and a wellness questionnaire (n = 11), and B) profiled the responses with acceptable reliability (no between-trial differences and between-day coefficient of variation (CV) ≤10% and intraclass correlation coefficient (ICC) ≥0.8) for 120 h (baseline: -3, +24, +48, +72, +96, +120 h) following RL match-play (n = 10). In part A, force at 200, and 250 ms, and peak force (PF) demonstrated acceptable within- (CV%: 3.67-8.41%, ICC: 0.89-0.93) and between-day (CV%: 4.34-8.62%, ICC: 0.87-0.92) reliability for IMTP. Most CMJ variables demonstrated acceptable within-day reliability (CV%: 3.03-7.34%, ICC: 0.82-0.98), but only six (i.e., flight-time, PF, peak power (PP), relative PP, velocity at take-off (VTO), jump-height (JH)) showed acceptable between-day reliability (CV%: 2.56-6.79%, ICC: 0.83-0.91). Only total wellness demonstrated acceptable between-day reliability (CV%: 7.05%, ICC: 0.90) from the questionnaire. In part B, reductions of 4.75% and 9.23% (vs. baseline; 2.54 m∙s-1; 0.33 m) occurred at +24 h for CMJ VTO, and JH, respectively. Acceptable reliability was observed in some, but not all, variables and the magnitude and time-course of post-match responses were test and variable specific. Practitioners should therefore be mindful of the influence that the choice of recovery monitoring tool may have upon the practical interpretation of the data.

The physical demands of professional soccer goalkeepers throughout a week-long competitive microcycle and transiently throughout match-play.

The physical demands of English Premier League soccer goalkeepers were quantified during training and match-play in a two-part study. Goalkeeper-specific micromechanical electrical systems (MEMS) devices, profiled training and match-day activities throughout one competitive week (n=8; part A). Changes in MEMS-derived outputs were also profiled throughout match-play (100 matches; n=8, 18±14 observations per goalkeeper; part B). In part A, goalkeeping-training elicited the most dives (51±11) versus all activities (all p≤0.030) except shooting-training (p=0.069). Small-sided games elicited the fewest (5±3) dives (all p≤0.012). High-speed distance covered in match (103±72 m) was similar to goalkeeping-training (p=0.484), while exceeding shooting-training, small-sided games, pre-match shooting, and pre-match warm-up (all p=0.012). Most changes of direction (34±12) and explosive efforts (70±18) occurred during goalkeeping-training, with values exceeding match (both p=0.012). In part B, between-half reductions in total distance, but increased high-speed changes of direction and explosive efforts, occurred (both p≤0.05). Excluding the number of high jumps, all variables differed from 0-15-min during at least one match epoch, with more dives (1.3±1.4 vs 1.0±1.1) and explosive efforts (2.5±2.4 vs 2.0±1.8) performed between 75-90-min versus 0-15-min (all p<0.05). These data highlight the differing physical demands of various activities performed by professional soccer goalkeepers throughout a competitive week.

Practitioner perceptions regarding the practices of soccer substitutes.

Despite empirical observations suggesting that practitioners value the use of substitutions during soccer match-play, limited research has sought to substantiate such claims. This study used online surveys to assess the perceptions of practitioners within professional soccer about the use and practices of substitutes. Thirty-three practitioners completed one of two surveys (each requiring both open and closed questions to be answered), depending upon whether their primary role related mostly to tactical ('tactical practitioners'; n = 7) or physical ('physical practitioners'; n = 26) aspects of player/team management. Thematic content analysis of responses identified four higher-order themes: 'impact of substitutions', 'planning and communication', 'player preparation and recovery' and 'regulations'. Eighty-five percent of practitioners believed that substitutes are important in determining success during soccer match-play, with the primary justification being the perceived ability of such players to provide a physical and/or tactical impact. However, contextual factors such as the match situation, timing of introduction, and players undergoing adequate pre-pitch-entry preparation, may be important for realising such aims. Although many practitioners believed that there was a need for substitutes to engage in bespoke non-match-day preparations and recovery strategies that differ from starting players, logistical considerations, such as scarcity of resources, often limit their scope. Notwithstanding, 96% of respondents indicated that substitutes frequently perform extra conditioning sessions to account for deficits in high-speed running loads compared with players exposed to a longer period of match-play. Substitutes' pre-match warm-ups are typically led by team staff, however practitioners reported providing varying levels of input with regards to the practices adopted between kick-off and pitch-entry. Uncertainty exists as to the efficacy of current pre-pitch-entry practices, and 100% of practitioners highlighted 'preparatory strategies' as at least a 'moderately important' direction for future research. This study presents novel insights and highlights areas that are considered future research priorities amongst those working in the field.

A match-day analysis of the movement profiles of substitutes from a professional soccer club before and after pitch-entry.

Whilst the movement demands of players completing a whole soccer match have been well-documented, comparable information relating to substitutes is sparse. Therefore, this study profiled the match-day physical activities performed by soccer substitutes, focusing separately on the pre and post pitch-entry periods. Seventeen English Championship soccer players were monitored using 10 Hz Micromechanical Electrical Systems (MEMS) devices during 13 matches in which they participated as substitutes (35 observations). Twenty physical variables were examined and data were organised by bouts of warm-up activity (pre pitch-entry), and five min epochs of match-play (post pitch-entry). Linear mixed modelling assessed the influence of time (i.e., 'bout' and 'epoch'), playing position, and match scoreline. Substitutes performed 3±1 rewarm-up bouts∙player-1∙match-1. Compared to the initial warm-up, each rewarm-up was shorter (-19.7 to -22.9 min) and elicited less distance (-606 to -741 m), whilst relative total distances were higher (+26 to +69 m∙min-1). Relative total (+13.4 m∙min-1) and high-speed (+0.4 m∙min-1) distances covered during rewarm-ups increased (p <0.001) with proximity to pitch-entry. Players covered more (+3.2 m; p = 0.047) high-speed distance per rewarm-up when the assessed team was losing compared with when winning at the time of pitch-entry. For 10 out of 20 variables measured after pitch-entry, values reduced from 0-5 min thereafter, and substitutes covered greater (p ˂0.05) total (+67 to +93 m) and high-speed (+14 to +33 m) distances during the first five min of match-play versus all subsequent epochs. Midfielders covered more distance (+41 m) per five min epoch than both attackers (p ˂0.001) and defenders (p = 0.016). Acknowledging the limitations of a solely movement data approach and the potential influence of other match-specific factors, such findings provide novel insights into the match-day demands faced by substitute soccer players. Future research opportunities exist to better understand the match-day practices of this population.

Match-Play and Performance Test Responses of Soccer Goalkeepers: A Review of Current Literature.

Goalkeepers are typically the last defensive line for soccer teams aiming to minimise goals being conceded, with match rules permitting ball handling within a specific area. Goalkeepers are also involved in initiating some offensive plays, and typically remain in close proximity to the goal line while covering ~ 50% of the match distances of outfield players; hence, the competitive and training demands of goalkeepers are unique to their specialised position. Indeed, isolated performance tests differentiate goalkeepers from outfield players in multiple variables. With a view to informing future research, this review summarised currently available literature reporting goalkeeper responses to: (1) match play (movement and skilled/technical demands) and (2) isolated performance assessments (strength, power, speed, aerobic capacity, joint range of motion). Literature searching and screening processes yielded 26 eligible records and highlighted that goalkeepers covered ~ 4-6 km on match day whilst spending ~ 98% of time at low-movement intensities. The most decisive moments are the 2-10 saves·match-1 performed, which often involve explosive actions (e.g. dives, jumps). Whilst no between-half performance decrements have been observed in professional goalkeepers, possible transient changes over shorter match epochs remain unclear. Isolated performance tests confirm divergent profiles between goalkeepers and outfield players (i.e. superior jump performance, reduced [Formula: see text]2max values, slower sprint times), and the training of soccer goalkeepers is typically completed separately from outfield positions with a focus primarily on technical or explosive drills performed within confined spaces. Additional work is needed to examine the physiological responses to goalkeeper-specific training and match activities to determine the efficacy of current preparatory strategies.

Profiling the Responses of Soccer Substitutes: A Review of Current Literature.

Depending upon competition regulations, the laws of soccer allow between three and an unlimited number of substitutions that can be made on either a permanent or rolling basis. Substitutes are typically introduced to minimise/offset the effects of fatigue, alter tactics, replace players deemed as underperforming or injured, and/or give playing time to youth players or to squad members returning from injury. While the match-day practices of substitutes include participation in the pre-match warm-up, and sporadic periods of rewarm-up activity, it is currently unclear as to whether these pre-entry preparations facilitate optimal match performance thereafter. Acknowledging the contextual factors that possibly influence substitutes' performance, this review summarises the presently available literature on soccer substitutes, and makes recommendations for future research. Literature searching and screening yielded 13 studies, which have typically focused on characterising: (1) the patterns, including timing, of substitutes' introduction; (2) indices of match-performance; and (3) the emotional experiences of soccer substitutes. The majority of substitutions occur after the first-half has ended (i.e. at half-time or during the second-half), with introduced players exceeding the second-half physical performances of those who started the match. Observations of progressive improvements in running performance as playing time increases, and findings that substitutes mostly experience negative emotions, highlight the potential inadequacies of pre-match preparations, and present future research opportunities. Additional work is therefore needed to confirm these findings and to determine the efficacy of current preparation strategies, thereby providing opportunities to assess then address substitutes' pre-pitch entry preparations, on-field performance and emotional responses.

A comparison of substrate oxidation during prolonged exercise in men at terrestrial altitude and normobaric normoxia following the coingestion of 13C glucose and 13C fructose.

This study compared the effects of coingesting glucose and fructose on exogenous and endogenous substrate oxidation during prolonged exercise at altitude and sea level, in men. Seven male British military personnel completed two bouts of cycling at the same relative workload (55% Wmax) for 120 min on acute exposure to altitude (3375 m) and at sea level (~113 m). In each trial, participants ingested 1.2 g·min-1 of glucose (enriched with 13C glucose) and 0.6 g·min-1 of fructose (enriched with 13C fructose) directly before and every 15 min during exercise. Indirect calorimetry and isotope ratio mass spectrometry were used to calculate fat oxidation, total and exogenous carbohydrate oxidation, plasma glucose oxidation, and endogenous glucose oxidation derived from liver and muscle glycogen. Total carbohydrate oxidation during the exercise period was lower at altitude (157.7 ± 56.3 g) than sea level (286.5 ± 56.2 g, P = 0.006, ES = 2.28), whereas fat oxidation was higher at altitude (75.5 ± 26.8 g) than sea level (42.5 ± 21.3 g, P = 0.024, ES = 1.23). Peak exogenous carbohydrate oxidation was lower at altitude (1.13 ± 0.2 g·min-1) than sea level (1.42 ± 0.16 g·min-1, P = 0.034, ES = 1.33). There were no differences in rates, or absolute and relative contributions of plasma or liver glucose oxidation between conditions during the second hour of exercise. However, absolute and relative contributions of muscle glycogen during the second hour were lower at altitude (29.3 ± 28.9 g, 16.6 ± 15.2%) than sea level (78.7 ± 5.2 g (P = 0.008, ES = 1.71), 37.7 ± 13.0% (P = 0.016, ES = 1.45). Acute exposure to altitude reduces the reliance on muscle glycogen and increases fat oxidation during prolonged cycling in men compared with sea level.

The Dangers of Estimating V˙O2max Using Linear, Nonexercise Prediction Models.

PURPOSE: This study aimed to compare the accuracy and goodness of fit of two competing models (linear vs allometric) when estimating V˙O2max (mL·kg·min) using nonexercise prediction models. METHODS: The two competing models were fitted to the V˙O2max (mL·kg·min) data taken from two previously published studies. Study 1 (the Allied Dunbar National Fitness Survey) recruited 1732 randomly selected healthy participants, 16 yr and older, from 30 English parliamentary constituencies. Estimates of V˙O2max were obtained using a progressive incremental test on a motorized treadmill. In study 2, maximal oxygen uptake was measured directly during a fatigue limited treadmill test in older men (n = 152) and women (n = 146) 55 to 86 yr old. RESULTS: In both studies, the quality of fit associated with estimating V˙O2max (mL·kg·min) was superior using allometric rather than linear (additive) models based on all criteria (R, maximum log-likelihood, and Akaike information criteria). Results suggest that linear models will systematically overestimate V˙O2max for participants in their 20s and underestimate V˙O2max for participants in their 60s and older. The residuals saved from the linear models were neither normally distributed nor independent of the predicted values nor age. This will probably explain the absence of a key quadratic age term in the linear models, crucially identified using allometric models. Not only does the curvilinear age decline within an exponential function follow a more realistic age decline (the right-hand side of a bell-shaped curve), but the allometric models identified either a stature-to-body mass ratio (study 1) or a fat-free mass-to-body mass ratio (study 2), both associated with leanness when estimating V˙O2max. CONCLUSIONS: Adopting allometric models will provide more accurate predictions of V˙O2max (mL·kg·min) using plausible, biologically sound, and interpretable models.

Multi-Stage 20-m Shuttle Run Fitness Test, Maximal Oxygen Uptake and Velocity at Maximal Oxygen Uptake.

The multi-stage 20-m shuttle run fitness test (20mMSFT) is a popular field test which is widely used to measure aerobic fitness by predicting maximum oxygen uptake (VO2max) and performance. However, the velocity at which VO2max occurs (vVO2max) is a better indicator of performance than VO2max, and can be used to explain inter-individual differences in performance that VO2max cannot. It has been reported as a better predictor for running performance and it can be used to monitor athletes' training for predicting optimal training intensity. This study investigated the validity and suitability of predicting VO2max and vVO2max of adult subjects on the basis of the performance of the 20mMST. Forty eight (25 male and 23 female) physical education students performed, in random order, a laboratory based continuous horizontal treadmill test to determine VO2max, vVO2max and a 20mMST, with an interval of 3 days between each test. The results revealed significant correlations between the number of shuttles in the 20mMSFT and directly determined VO2max (r = 0.87, p<0.05) and vVO2max (r = 0.93, p<0.05). The equation for prediction of VO2max was y = 0.0276x + 27.504, whereas for vVO2max it was y = 0.0937x + 6.890. It can be concluded that the 20mMSFT can accurately predict VO2max and vVO2max and this field test can provide useful information regarding aerobic fitness of adults. The predicted vVO2max can be used in monitoring athletes, especially in determining optimal training intensity.

The effect of wave conditions and surfer ability on performance and the physiological response of recreational surfers.

This study investigated the effects of wave conditions on performance and the physiological responses of surfers. After institutional ethical approval 39 recreational surfers participated in 60 surfing sessions where performance and physiological response were measured using global positioning system (GPS) heart rate monitors. Using GPS, the percentage time spent in surfing activity categories was on average 41.6, 47.0, 8.1, and 3.1% for waiting, paddling, riding, and miscellaneous activities, respectively. Ability level of the surfers, wave size, and wave period are significantly associated with the physiological, ride, and performance parameters during surfing. As the ability level of the surfers increases there is a reduction in the relative exercise intensity (e.g., average heart rate as a percentage of laboratory maximum, rpartial = -0.412, p < 0.01) which is in contrast to increases in performance parameters (e.g., maximum ride speed (0.454, p < 0.01). As the wave size increased there were reductions in physiological demand (e.g., total energy expenditure rpartial = -0.351, p ≤ 0.05) but increases in ride speed and distance measures (e.g., the maximum ride speed, 0.454, p < 0.01). As the wave period increased there were increases in intensity (e.g., average heart rate as a percentage of laboratory maximum, rp = 0.490, p < 0.01) and increases in ride speed and distance measures (e.g., the maximum ride speed, rpartial = 0.371, p < 0.01). This original study is the first to show that wave parameters and surfer ability are significantly associated with the physiological response and performance characteristics of surfing.

The effect of pre-exercise galactose and glucose ingestion on high-intensity endurance cycling.

This study evaluated the effects of the pre-exercise (30 minutes) ingestion of galactose (Gal) or glucose (Glu) on endurance capacity as well as glycemic and insulinemic responses. Ten trained male cyclists completed 3 randomized high-intensity cycling endurance tests. Thirty minutes before each trial, cyclists ingested 1 L of either 40 g of glucose, 40 g of galactose, or a placebo in a double-blind manner. The protocol comprised 20 minutes of progressive incremental exercise (70-85% maximal power output [Wmax]); ten 90-second bouts at 90% Wmax, separated by 180 seconds at 55% Wmax; and 90% Wmax until exhaustion. Blood samples were drawn throughout the protocol. Times to exhaustion were longer with Gal (68.7 ± 10.2 minutes, p = 0.005) compared with Glu (58.5 ± 24.9 minutes), with neither being different to placebo (63.9 ± 16.2 minutes). Twenty-eight minutes after Glu consumption, plasma glucose and serum insulin concentrations were higher than with Gal and placebo (p < 0.001). After the initial 20 minutes of exercise, plasma glucose concentrations increased to a relative hyperglycemia during the Gal and placebo, compared with Glu condition. Higher plasma glucose concentrations during exercise, and the attenuated serum insulin response at rest, may explain the significantly longer times to exhaustion produced by Gal compared with Glu. However, neither carbohydrate treatment produced significantly longer times to exhaustion than placebo, suggesting that the pre-exercise ingestion of galactose and glucose alone is not sufficient to support this type of endurance performance.

Preexercise galactose and glucose ingestion on fuel use during exercise.

PURPOSE: This study determined the effect of ingesting galactose and glucose 30 min before exercise on exogenous and endogenous fuel use during exercise. METHODS: Nine trained male cyclists completed three bouts of cycling at 60% W(max) for 120 min after an overnight fast. Thirty minutes before exercise, the cyclists ingested a fluid formulation containing placebo, 75 g of galactose (Gal), or 75 g of glucose (Glu) to which (13)C tracers had been added, in a double-blind randomized manner. Indirect calorimetry and isotope ratio mass spectrometry were used to calculate fat oxidation, total carbohydrate (CHO) oxidation, exogenous CHO oxidation, plasma glucose oxidation, and endogenous liver and muscle CHO oxidation rates. RESULTS: Peak exogenous CHO oxidation was significantly higher after Glu (0.68 ± 0.08 g.min(-1), P < 0.05) compared with Gal (0.44 ± 0.02 g.min(-1)); however, mean rates were not significantly different (0.40 ± 0.03 vs. 0.36 ± 0.02 g.min(-1), respectively). Glu produced significantly higher exogenous CHO oxidation rates during the initial hour of exercise (P < 0.01), whereas glucose rates derived from Gal were significantly higher during the last hour (P < 0.01). Plasma glucose and liver glucose oxidation at 60 min of exercise were significantly higher for Glu (1.07 ± 0.1 g.min(-1), P < 0.05, and 0.57 ± 0.08 g.min(-1), P < 0.01) compared with Gal (0.64 ± 0.05 and 0.29 ± 0.03 g.min(-1), respectively). There were no significant differences in total CHO, whole body endogenous CHO, muscle glycogen, or fat oxidation between conditions. CONCLUSION: The preexercise consumption of Glu provides a higher exogenous source of CHO during the initial stages of exercise, but Gal provides the predominant exogenous source of fuel during the latter stages of exercise and reduces the reliance on liver glucose.