Kathryn L. Weston

A comprehensive allometric analysis of 2nd digit length to 4th digit length in humans

It has been widely reported that men have a lower ratio of the 2nd and 4th human finger lengths (2D : 4D). Size-scaling ratios, however, have the seldom-appreciated potential for providing biased estimates. Using an information-theoretic approach, we compared 12 candidate models, with different assumptions and error structures, for scaling untransformed 2D to 4D lengths from 154 men and 262 women. In each hand, the two-parameter power function and the straight line with intercept models, both with normal, homoscedastic error, were superior to the other models and essentially equivalent to each other for normalizing 2D to 4D lengths. The conventional 2D : 4D ratio biased relative 2D length low for the generally bigger hands of men, and vice versa for women, thereby leading to an artefactual indication that mean relative 2D length is lower in men than women. Conversely, use of the more appropriate allometric or linear regression models revealed that mean relative 2D length was, in fact, greater in men than women. We conclude that 2D does not vary in direct proportion to 4D for both men and women, rendering the use of the simple 2D : 4D ratio inappropriate for size-scaling purposes and intergroup comparisons.

Acute cardiorespiratory, perceptual and enjoyment responses to high-intensity interval exercise in adolescents

Abstract This study aimed to examine adolescents’ acute cardiorespiratory and perceptual responses during high-intensity interval exercise (HIIE) and enjoyment responses following HIIE and work-matched continuous moderate intensity exercise (CMIE). Fifty-four 12- to 15-year olds (27 boys) completed 8 × 1-min cycling at 90% peak power with 75-s recovery (HIIE) and at 90% of the gas exchange threshold (CMIE). Absolute oxygen uptake (), percentage of maximal (%), heart rate (HR), percentage of maximal HR (%HRmax) and ratings of perceived exertion (RPE) were collected during HIIE. Enjoyment was measured using the physical activity enjoyment scale (PACES) following HIIE and CMIE. Boys elicited higher absolute during HIIE work (p < .01, effect size (ES) > 1.22) and recovery (p < .02, ES > 0.51) intervals but lower % during HIIE recovery intervals compared to girls (p < .01, ES > 0.67). No sex differences in HR and %HRmax were evident during HIIE and 48 participants attained ≥90% HRmax. Boys produced higher RPE at intervals 6 (p = .004, ES = 1.00) and 8 (p = .003, ES = 1.00) during HIIE. PACES was higher after HIIE compared with CMIE (p = .003, ES = 0.58). Items from PACES “I got something out of it”, “It’s very exciting” and “It gives me a strong feeling of success” were higher after HIIE (all p < .01, ES > 0.32). The items “I feel bored” and “It’s not at all interesting” were higher after CMIE (all p < .01, ES > 0.46). HIIE elicits a maximal cardiorespiratory response in most adolescents. Greater enjoyment after HIIE was due to elevated feelings of reward, excitement and success and may serve as a strategy to promote health in youth.

Effect of novel, school-based High-intensity Interval Training (HIT) on cardiometabolic health in adolescents: Project FFAB (Fun Fast Activity Blasts) - An exploratory controlled before-and-after trial

Background Low-volume high-intensity interval training holds promise for cardiometabolic health promotion in adolescents, but sustainable interventions must be practical and engaging. We examined the effect of a school-based multi-activity low-volume high-intensity interval training intervention on adolescents’ cardiometabolic health. Methods In an exploratory controlled before-and-after design, 101 adolescents (mean age ± standard deviation [SD] 14.0 ± 0.3 years) were recruited from four schools; two were designated as intervention sites (n = 41), and two as control (n = 60). The intervention comprised 4 to 7 repetitions of 45 s maximal effort exercise (basketball, boxing, dance and soccer drills) interspersed with 90-s rest, thrice weekly for 10 weeks. Outcomes were non-fasting blood lipids and glucose, waist circumference, high sensitivity C-reactive protein, resting blood pressure, physical activity, twenty-metre shuttle-run test performance and carotid artery intima-media thickness. The difference in the change from baseline (intervention minus control) was estimated for each outcome. Using magnitude-based inferences, we calculated the probability that the true population effect was beneficial, trivial, and harmful against a threshold for the minimum clinically important difference of 0.2 between-subject SDs. Results and Discussion Mean (± SD) attendance for the intervention (expressed as percentage of available intervention sessions [n = 30]) was 77 ± 13%. Post-intervention, there were likely beneficial effects for triglycerides (-26%; 90% confidence interval -46% to 0%), waist circumference (-3.9 cm; -6.1 cm to -1.6 cm) and moderate-to-vigorous physical activity (+16 min; -5 to 38 min), and a possibly beneficial effect for twenty-metre shuttle-run test performance (+5 shuttles; -1 to 11 shuttles) in intervention participants (vs controls). The role of elevated triglycerides and waist circumference in cardiovascular disease and metabolic syndrome development underlines the importance of our findings. We also demonstrated that school-based low-volume high-intensity interval training can be delivered as intended, thus representing a novel and scalable means of improving aspects of adolescents’ cardiometabolic health. Trial Registration ClinicalTrials.gov NCT02626767

Short- and long-term reliability of leg extensor power measurement in middle-aged and older adults

ABSTRACT Muscular power is important for maintaining physical functioning with aging. Proper quantification of the reliability of muscular power tests is crucial to inform monitoring of individuals and sample size planning for interventional studies. This study evaluated short- and long-term reliability of leg extensor power measurement in 72 adults (age 62.7 ± 8.6 years). Participants completed four repeat trials on the Nottingham leg extensor power rig, with a further trial twelve weeks later. Mean change, typical error, and intraclass correlation coefficients (ICC) were calculated. For short-term reliability, mean change in power output was trivial after two trials (1.2–4.8%). Typical errors were small following four trials in the dominant leg of males (10.9–5.8%), three in the non-dominant leg of males (9.9–6.2%) and the dominant leg of females (10.0–9.6%) and two in the non-dominant leg in females (8.3%). Intraclass correlation coefficients (ICCs) were very high (0.88–0.96). For long-term reliability, mean change remained trivial (1.0–2.5%), typical errors remained small (5.8–8.6%), and ICCs very high (0.94–0.96). The leg extensor power rig is a reliable method for assessing lower body muscular power, both short- and long-term, with only minimal habituation effects.

Perspectives on high-intensity interval exercise for health promotion in children and adolescents

Physical activity lowers future cardiovascular disease (CVD) risk; however, few children and adolescents achieve the recommended minimum amount of daily activity. Accordingly, there is virtue in identifying the efficacy of small volumes of high-intensity exercise for health benefits in children and adolescents for the primary prevention of CVD risk. The purpose of this narrative review is to provide a novel overview of the available literature concerning high-intensity interval-exercise (HIIE) interventions in children and adolescents. Specifically, the following areas are addressed: 1) outlining the health benefits observed following a single bout of HIIE, 2) reviewing the role of HIIE training in the management of pediatric obesity, and 3) discussing the effectiveness of school-based HIIE training. In total, 39 HIIE intervention studies were included in this review. Based upon the available data, a single bout of high-intensity exercise provides a potent stimulus for favorable, acute changes across a range of cardiometabolic outcomes that are often superior to a comparative bout of moderate-intensity exercise (14 studies reviewed). HIIE also promotes improvements in cardiorespiratory fitness and cardiometabolic health status in overweight and obese children and adolescents (10 studies reviewed) and when delivered in the school setting (15 studies reviewed). We thus conclude that high-intensity exercise is a feasible and potent method of improving a range of cardiometabolic outcomes in children and adolescents. However, further work is needed to optimize the delivery of HIIE interventions in terms of participant enjoyment and acceptability, to include a wider range of health outcomes, and to control for important confounding variables (eg, changes in diet and habitual physical activity). Finally, research into the application of HIIE training interventions to children and adolescents of different ages, sexes, pubertal status, and sociocultural backgrounds is required.

Perceptual Responses to High- and Moderate-intensity Interval Exercise in Adolescents

Purpose Continuous high-intensity exercise is proposed to evoke unpleasant sensations as predicted by the dual-mode theory and may negatively impact on future exercise adherence. Previous studies support unpleasant sensations in affective responses during continuous high-intensity exercise, but the affect experience during high-intensity interval exercise (HIIE) involving brief bursts of high-intensity exercise separated by low-intensity activity is poorly understood in adolescents. We examined the acute affective, enjoyment, and perceived exertion responses to HIIE compared with moderate-intensity interval exercise (MIIE) in adolescents. Methods Thirteen adolescent boys (mean ± SD: age, 14.0 ± 0.5 yr) performed two counterbalanced exercise conditions: 1) HIIE: 8 × 1-min work intervals at 90% maximal aerobic speed; and 2) MIIE: between 9 and 12 × 1-min work intervals at 90% ventilatory threshold where the number of intervals performed were distance-matched to HIIE. HIIE and MIIE work intervals were interspersed with 75 s active recovery at 4 km·h−1. Affect, enjoyment, and RPE were recorded before, during, and after exercise. Results Affect responses declined in both conditions but the fall was greater in HIIE than MIIE (P < 0.025, effect size [ES], 0.64 to 0.81). Affect remained positive at the end-work interval for both conditions (MIIE, 2.62 ± 1.50; HIIE, 1.15 ± 2.08 on feeling scale). No enjoyment differences were evident during HIIE and MIIE (P = 0.32), but HIIE elicited greater postexercise enjoyment compared with MIIE (P = 0.01, ES = 0.47). RPE was significantly higher during HIIE than MIIE across all work intervals (all P < 0.03, ES > 0.64). Conclusions Despite elevated RPE, HIIE did not elicit prominent unpleasant feelings as predicted by the dual-mode theory and was associated with greater postexercise enjoyment responses than MIIE. This study demonstrates the feasibility of the application of HIIE as an alternative form of physical activity in adolescents.

Perceptual and prefrontal cortex haemodynamic responses to high-intensity interval exercise with decreasing and increasing work-intensity in adolescents

OBJECTIVES Affect experienced during high-intensity interval exercise (HIIE) is dependent on work-intensity, but the influence of increasing (low-to-high (L-H)) or decreasing (high-to-low (H-L)) work-intensity during HIIE remains unclear in adolescents. The role of prefrontal cortex haemodynamics in mediating changes in affect during HIIE also remains unexplored in adolescents. We examined affect, enjoyment and cerebral haemodynamic responses to HIIE with increasing or decreasing work intensities in adolescents. METHODS Participants (N = 16; 8 boys; age 12.5 ± 0.8 years) performed, on separate days, HIIE cycling consisting of 8 × 1-min work-intervals at 100%-to-70% (HIIEH-L), 70%-to-100% (HIIEL-H) or 85% (HIIECON) peak power separated by 75 s recovery. Affect, enjoyment and cerebral haemodynamics (oxygenation (∆O2Hb), deoxygenation (∆HHb) and tissue oxygenation index (TOI)) were recorded before, during, and after all conditions. RESULTS Affect and enjoyment were lower during HIIEH-L compared to HIIEL-H and HIIECON at work-intervals 1 to 3 (all P < 0.043, ES > 0.83) but were greater during HIIEH-L than HIIEL-H and HIIECON at work-interval 8 (all P < 0.048, ES > 0.83). ∆O2Hb was similar across conditions (P = 0.87) but TOI and ∆HHb were significantly greater and lower, respectively during HIIEH-L compared to HIIEL-H and HIIECON at work-interval 8 (all P < 0.039, ES > 0.40). Affect was correlated with TOI (all r > 0.92) and ∆HHb (all r > -0.73) across conditions. CONCLUSIONS HIIEH-L offers advancement to the HIIECON and HIIEL-H which bring significant greater affect and enjoyment towards the end HIIE work-interval, implicating the feasibility and adoption of this protocol for health promotion in youth. Also, changes in prefrontal cortex haemodynamics are associated with the affect during HIIE.

ALLOMETRIC SCALING OF VO2max: A SYSTEMATIC REVIEW AND META-ANALYSIS

We aimed to provide the first quantitative synthesis of derived static allometric coefficients (b) used for scaling maximal oxygen uptake (VO2max) to whole-body mass and fat-free mass in human samples. Eight electronic databases were searched for relevant peer-reviewed articles. Inclusion criteria comprised human cardiorespiratory fitness data; cross-sectional study designs; an empirical derivation of the exponent; reported precision statistics; and reported information regarding participant sex, age and sports background, VO2max protocol, body composition protocol and line-fitting methods. Thirty-seven studies, involving 7,851 participants, met the eligibility criteria and were dichotomized into two main domains relevant to whole-body mass (n=28) and fat-free mass (n=16), respectively. The pooled allometric exponent (95% CL) was found to be 0.71 (0.65 to 0.77) for body mass and 0.91 (0.83 to 0.98) for fat-free mass. The among-studies heterogeneity was substantial for both whole-body mass and fat-free mass (τ =±0.15). Participant sex explained 33% of the between-study variability in the whole body mass exponent, but only 5% of the variability in the fat-free mass exponent. While the body mass exponent was substantially lower in women (b=0.52; 95% CL: 0.41 to 0.64) than for men (b=0.77; 95% CL: 0.71 to 0.83), the fat-free mass exponent was similar for both sexes. None of the identified moderator variables was statistically significant. The body mass exponent estimate encompassed both ⅔- and ¾-power laws. Conversely, the fat-free mass exponent was substantially larger and more generalisable due to the heterogeneity of body composition in human samples. We conclude that the scaling of VO2max in humans is consistent with the allometric cascade model, with an estimated pooled exponent that precludes ⅔- and ¾-power scaling.

THE QUANTIFICATION OF CHANGES IN CARDIORESPIRATORY FITNESS INDEPENDENT FROM CHANGES IN BODY MASS: ILLUSTRATION OF AN ALLOMETRIC APPROACH

Both obesity and a low level of cardiorespiratory fitness (VO2max) are strong predictors of morbidity and mortality. Therefore, in any lifestyle intervention study, it is important to ascertain if any changes in VO2max are clinically important, while considering any parallel changes in body mass and/or composition. Most researchers adopt a simple ratiometric approach to normalising VO2max (ml·kg−1·min−1), even though this is associated with several important assumptions, which are rarely confirmed by researchers. Using data from the Activity Counselling Trial (ACT), we developed and applied a novel allometric approach for comparing normalised changes in VO2max between different treatment arms. Overall, 874 participants were randomly allocated into advice only (n=292), assistance (n=293) and counselling group (n=289), respectively. A repeated-measures allometric model was adopted to adjust the changes in VO2max for the concurrent changes in body mass and fat-free mass from baseline to 24-month follow-up. Magnitude thresholds for standardized differences in VO2max of 0.20, 0.60, 1.20, 2.0 and 4.0 were considered as a small, moderate, large, very large and extremely large effect, respectively. The within-subjects allometric exponent (90% CL) for body mass was 0.46 (0.40 to 0.53) and 0.37 (0.31 to 0.43) in men and women, respectively. The respective fat-free mass exponents were 0.79 (0.71 to 0.87) and 0.64 (0.56 to 0.73). Ratio-scaled VO2max increased 4.5% (2.1% to 7.0%) more in the assistance vs advice group. This increase was slightly smaller when allometrically scaled to body mass [3.9% (1.7% to 6.1%)] and fat-free mass [3.7% (1.5% to 6.0%)], although standardised mean differences were similar between approaches (≈ 0.2). Similar findings were obtained for the counselling vs advice groups. Changes in VO2max were small in all study arms for men. Contrary to the original study report and subsequent citations, scaled intervention effects on cardiorespiratory fitness in the ACT are unlikely to be clinically important. Given the non-linear relationship between changes in body size and VO2max, a within-subjects allometric modelling approach is recommended for accurately quantifying any intervention-induced effects in future studies.