Scaling Submaximal Exercise Cardiac Output and Stroke Volume: The HERITAGE Family Study

Allometric exponents for scaling running economy in human samples: A systematic review and meta-analysis

Ratio-scaled VO2 is the widely used method for quantifying running economy (RE). However, this method should be criticized due to its theoretical defect and curvilinear relationship indicated by the allometric scaling, although no consensus has been achieved on the generally accepted exponent b value of body weight. Therefore, this study aimed to provide a quantitative synthesis of the reported exponents used to scale VO2 to body weight. Six electronic databases were searched based on related terms. Inclusion criteria involved human cardiopulmonary testing data, derived exponents, and reported precision statistics. The random-effects model was applied to statistically analyze exponent b. Subgroup and meta-regression analyses were conducted to explore the potential factors contributing to variation in b values. The probability of the true exponent being below 1 in future studies was calculated. The estimated b values were all below 1 and aligned with the 3/4 power law, except for the 95 % prediction interval of the estimated fat-free body weight exponent b. A publication bias and a slightly greater I2 and τ statistic were also observed in the fat-free body weight study cohort. The estimated probabilities of the true body weight exponent, full body weight exponent, and fat-free body weight exponent being lower than 1 were 93.8 % (likely), 95.1 % (very likely), and 94.5 % (likely) respectively. 'Sex difference', 'age category', 'sporting background', and 'testing modality' were four potential but critical variables that impacted exponent b. Overall, allometric-scaled RE should be measured by full body weight with exponent b raised to 3/4.

Scaling VO2max to body size differences to evaluate associations to CVD incidence and all-cause mortality risk

Objective

To evaluate and compare ratio and allometric scaling models of maximal oxygen consumption (VO₂max) for different body size measurements in relation to cardiovascular disease (CVD) incidence and all-cause mortality.

Methods

316 116 individuals participating in occupational health screenings, initially free from CVD, were included. VO₂max was estimated using submaximal cycle test. Height, body mass and waist circumference (WC) were assessed, and eight different scaling models (two evaluated in a restricted sample with WC data) were derived. Participants were followed in national registers for first-time CVD event or all-cause mortality from their health screening to first CVD event, death or 31 December 2015.

Results

Increasing deciles of VO₂max showed lower CVD risk and all-cause mortality for all six models in the full sample (p<0.001) as well as with increasing quintiles in the restricted sample (eight models) (p<0.001). For CVD risk and all-cause mortality, significantly weaker associations with increasing deciles for models 1 (L·min⁻¹) and 5 (mL·min⁻¹·height⁻²) were seen compared with model 2 (mL·min⁻¹·kg⁻¹), (CVD, p<0.00001; p<0.00001: all-cause mortality, p=0.008; p=0.001) and in some subgroups. For CVD, model 6 (mL·min⁻¹·(kg¹·height⁻¹)⁻¹) had a stronger association compared with model 2 (p<0.00001) and in some subgroups.

In the restricted sample, trends for significantly stronger associations for models including WC compared with model 2 were seen in women for both CVD and all-cause mortality, and those under 50 for CVD.

Conclusion

In association to CVD and all-cause mortality, only small differences were found between ratio scaling and allometric scaling models where body dimensions were added, with some stronger associations when adding WC in the models.

Effect of Aerobic Exercise Intensity on Energy Expenditure and Weight Loss in Severe Obesity-A Randomized Controlled Trial

OBJECTIVE

This study aimed to compare the effects of two aerobic exercise programs of different intensities on energy expenditure.

METHODS

This was a single-center randomized controlled trial of patients with severe obesity allocated to a 24-week moderate-intensity continuous training (MICT) program or a combined MICT with high-intensity interval training (HIIT/MICT) program. The primary outcome was energy expenditure during exercise (EEDE). Secondary outcomes included resting metabolic rate, cardiorespiratory fitness, and body composition.

RESULTS

A total of 82 (56% females) patients were screened, and 71 (55% females) patients were allocated to HIIT/MICT (n = 37) or MICT (n = 34). Per-protocol analysis showed that EEDE increased by 10% (95% CI: 3%-17%) in the HIIT/MICT group (n = 16) and 7.5% (95% CI: 4%-10%) in the MICT group (n = 24), with no differences between groups. In the 8- to 16- week per-protocol analysis, the HIIT/MICT group had a significantly larger increase in EEDE compared with the MICT group. Resting metabolic rate remained unchanged in both groups. HIIT/MICT and MICT were associated with significant weight loss of 5 kg and 2 kg, respectively.

CONCLUSIONS

Patients completing a 24-week combined HIIT/MICT program did not achieve a higher EEDE compared with those who completed a 24-week MICT program. The HIIT/MICT group experienced, on average, a 3-kg-larger weight loss than the MICT group.

Associations between cardiorespiratory fitness and weight loss in patients with severe obesity undergoing an intensive lifestyle intervention program: retrospective cohort study

BACKGROUND

To assess the association between cardiorespiratory fitness (CRF) and weight changes in treatment seeking patients with severe obesity who underwent a 1-year intensive lifestyle intervention (ILI) program.

METHODS

Retrospective cohort study conducted at a tertiary care outpatient rehabilitation center from November 1, 2013 through January 1, 2017. CRF was measured as maximal oxygen consumption during a maximal oxygen uptake (VO_2max) test on a treadmill or bicycle at baseline and after 3 months.

RESULTS

A total of 180 patients had a baseline mean (SD) BMI 41.1 (4.8) kg/m² and CRF of 79.4 (14.9) mL·kg^-0.75·min^- 1. Patients with a baseline CRF above median achieved a greater 3-month and 1-year weight loss compared with patients with CRF below median; mean (95% CI) 2.5 kg (1.3, 3.8) and 4.0 kg (0.8, 7.2), respectively. In addition, patients with 3-month changes of CRF above median had 4.0 kg (0.9, 7.1) greater weight loss at 1-year follow-up than those below median.

CONCLUSIONS

Among patients with severe obesity who underwent a 1-year ILI program, higher baseline CRF was associated with significantly larger weight loss after 3 months and 1 year. In addition, those with higher initial 3-month CRF changes had greater weight loss at 1 year.

TRIAL REGISTRATION

Retrospectively registered in Regional Committees for Medical and Health Research Ethics (REC) south east September 22, 2016 (2016/1414) and clinicaltials.gov August 13, 2018 (identifier: NCT03593798 ).

Maximal cardiac output in athletes: influence of age

BACKGROUND

The decline in maximal oxygen consumption (VO2max) with age seems to be exacerbated in endurance-trained athletes (EA) relative to untrained healthy subjects. Whether maximal cardiac output (Qmax) parallels this group-specific decline with age remains uncertain. Therefore, we sought to systematically review the literature and determine whether Qmax is similarly enhanced in EA across all ages relative to age-matched untrained counterparts.

DESIGN AND METHODS

We conducted a systematic search of MEDLINE, Cochrane and Web of Science from their inceptions until June 2014 for articles evaluating Qmax in athletes. A meta-analysis was performed to determine the standardized mean difference (SMD) in Qmax between EA and age-matched untrained healthy subjects. Included studies had to (i) comprise EA and control groups matched for body size or (ii) present Qmax values normalized for body size. Subgroup and meta-regression analyses were used to study the influence of age and potential moderating factors.

RESULTS

Eighteen studies were selected after systematic review, comprising 268 EA and 232 age-matched untrained subjects. Nine studies involved young EA (mean age ≤40 years) while nine studies involved master EA (mean age >55 years). After data pooling, young and master EA groups showed higher Qmax compared with control groups (SMD = 1.49 and SMD = 1.68, respectively; both p < 0.0001). The SMD in Qmax between EA and control groups was similar in studies in young EA compared with studies in master EA (p = 0.61). Moreover, the SMD in VO2max between EA and control groups did not differ in studies in young EA compared with studies in master EA (p = 0.37). In meta-regression analyses, the difference in percentage of body fat between EA and control groups was inversely associated with the SMD in Qmax (B = - 0.17, p = 0.01) and the SMD in VO2max (B = -0.20, p = 0.01). Mean age was not associated with the SMD in Qmax (B = -0.001, P = 0.90) nor with the SMD in VO2max (B = 0.01, P = 0.58).

CONCLUSIONS

Based on current published studies, the enhanced Qmax observed in EA compared with untrained healthy subjects matched for body size is not affected by age but may be related, at least in part, to the improved body composition of EA.

Does size matter? Clinical applications of scaling cardiac size and function for body size

Extensive evidence is available that cardiovascular structure and function, along with other biological properties that span the range of organism size and speciation, scale with body size. Although appreciation of such factors is commonplace in pediatrics, cardiovascular measurements in the adult population, with similarly wide variation in body size, are rarely corrected for body size. In this review, we describe the critical role of body size measurements in cardiovascular medicine. Using examples, we illustrate the confounding effects of body size. Current cardiovascular scaling practices are reviewed, as are limitations and alternative relationships between body and cardiovascular dimensions. The experimental evidence, theoretical basis, and clinical application of scaling of various functional parameters are presented. Appropriately scaled parameters aid diagnostic and therapeutic decision making in specific disease states such as hypertrophic cardiomyopathy and congestive heart failure. Large-scale studies in clinical populations are needed to define normative relationships for this purpose. Lack of appropriate consideration of body size in the evaluation of cardiovascular structure and function may adversely affect recognition and treatment of cardiovascular disease states in the adult patient.

Longitudinal plane colour tissue-Doppler myocardial velocities and their association with left ventricular length, volume, and mass in humans

AIMS

We investigated the relationships between colour tissue-Doppler parameters of left ventricular (LV) function and indices of LV morphology.

METHODS AND RESULTS

LV length, end-diastolic volume, and mass were assessed in 40 healthy adult subjects. Further, colour tissue-Doppler scans assessed peak myocardial velocities during systole (S') and early diastole (E') as well as acceleration during isovolumic contraction (IVCa) at the mitral annulus. Non-linear allometric relationships (Y = aX(b)) were calculated to provide size exponents (b), with 95% confidence intervals, for tissue-Doppler variables (Y) and LV morphology parameters (X). The b exponents for LV length with Peaks S' and E' were not substantially different from unity (b = 0.87 and 0.95, respectively, P > 0.05). Peak E' was also associated with LV volume (b = 0.39, r = 0.53, P < 0.05). IVCa was not related to any LV morphology parameter.

CONCLUSION

Peak S' or E' divided by LV length was confirmed as a valid size-independent scaling index. Conversely, IVCa is seemingly size independent.