Key points Exercise is considered medicine; however, the individual degree of responsiveness to a standardized dose of exercise is idiosyncratic. Individual responsiveness between distinct exercise modalities and the genetic/environmental contributions to exercise response are not well understood. In this novel randomized cross‐over design study, monozygotic and dizygotic twins, as pairs, underwent 3 months of resistance and endurance training, separated by a 3 month washout period, aiming to assess training responses in strength and fitness outcomes to dichotomous training modalities, as well as the genetic/environmental contributions to exercise response. Our findings indicate that (i) individual responsiveness differs between exercise modalities; (ii) low‐responders to one mode may be ‘rescued’ by switching to an alternate mode of exercise; and (iii) genes may not play as large a role, as previously estimated from cross‐sectional data, for exercise training adaptation. The present study has implications for those charged with optimizing the benefits of exercise by means of individualizing the exercise prescription. Abstract Exercise response is idiosyncratic, although the degree of responsiveness, concordance in response between modalities and genetic contribution to responsiveness are not well understood. We investigated this using a novel randomized cross‐over design of dichotomous exercise interventions in mono‐(MZ) and di‐zygotic (DZ) twin pairs. We studied strength (1RM) and fitness (V̇O2max) responses in 84 same‐sex untrained twins (30 MZ, 12 DZ pairs; 24.9 ± 5.4 years). Twins, as pairs, underwent 3 months of resistance (RES) and endurance (END) training, separated by a 3 month washout period. Training responses and genetic/environmental contributions to responses were assessed. Leg strength 1RM increased following RES but not END (△47 ± 29 vs. 3 ± 26 kg; P < 0.001), whereas V̇O2max increased following END but not RES (△0.25 ± 0.26 vs. 0.04 ± 0.25 L min−1; P < 0.001). A higher percentage of individuals responded to RES for strength and to END for V̇O2max (P < 0.0001). Within‐individual responses to each mode were not correlated (P > 0.05). Cross‐sectional intraclass correlations were higher for MZ than DZ pairs for all variables, largely as a result of shared environment. Following training, MZ, but not DZ pairs, were significantly correlated for strength change to RES (rMZ = 0.62, P = 0.002) and END (rMZ = 0.36, P = 0.04), and for V̇O2max change to END (L min−1, rMZ = 0.45, P = 0.02) with a mixture of unshared/shared environmental contributions. Our findings indicate that individual responsiveness differs between modalities and low‐responders to one mode may be ‘rescued’ by switching to an alternate mode. Additionally, genes may not play as large a role as previously estimated from cross‐sectional data for training adaptation, and/or cross‐sectional data do not reflect longitudinal training effects. The present study has implications for optimizing the individualization of exercise prescription.

There is acknowledged variability in the Circle of Willis in the general population, yet the structure and function relationship of the cerebrovasculature is poorly understood. We aimed to demonstrate the feasibility of combining high resolution imaging techniques and computational fluid dynamics (CFD) to describe cerebrovascular structure and function in vivo. We examined the null hypothesis that monozygotic (MZ) twins (18-30yrs) would exhibit similar CoW structure and function. Six twin pairs underwent 3T magnetic resonance angiography of the head and neck and B-mode Doppler ultrasound for velocity and diameter recordings in the vertebral and internal carotid arteries under three conditions (rest, hypercapnia and exercise). Artery diameter, length, tortuosity and bifurcation angle were assessed in regions of interest of the CoW. CFD simulated hemodynamics to determine the cardiac-cycle time averaged wall shear stress (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT). We observed low and insignificant intra-class correlations (ICC) between twins in all regions for diameter (ICC range 0.000-0.657, P>0.05), two of four regions for length (ICC range 0.355-0.368, P>0.05), all regions for tortuosity (ICC range 0.270-0.505, P>0.05), and all bifurcation angles (ICC range 0.000-0.547, P> 0.05). Similarly, no significant correlations were apparent for cerebral blood flow or CFD-derived measures of TAWSS, OSI and RRT, at rest or in response to hypercapnia or exercise. Therefore differences exist in CoW structure and associated shear stress in response to physiological stimulation. These data suggest that the structure, function and health of cerebrovascular arteries are not primarily genetically dependent.

Cocoa contains polyphenols that are thought to be beneficial for vascular health. We assessed the impact of chocolate containing distinct concentrations of cocoa on cerebrovascular function and cognition. Using a counterbalanced within-subject design, we compared the acute impact of consumption of energy-matched chocolate containing 80%, 35%, and 0% single-origin cacao on vascular endothelial function, cognition, and cerebrovascular function in 12 healthy postmenopausal women (mean ± SD age: 57.3 ± 5.3 y). Participants attended a familiarization session, followed by 3 experimental trials, each separated by 1 wk. Outcome measures included cerebral blood flow velocity (CBF) responses, recorded before and during completion of a computerized cognitive assessment battery (CogState); brachial artery flow-mediated dilation (FMD); and hemodynamic responses (heart rate and blood pressure). When CBF data before and after chocolate intake were compared between conditions through the use of 2-factor ANOVA, an interaction effect ( = 0.003) and main effects for chocolate ( = 0.043) and time ( = 0.001) were evident. Post hoc analysis revealed that both milk chocolate (MC; 35% cocoa; = 0.02) and dark chocolate (DC; 80% cocoa; = 0.003) induced significantly lower cerebral blood flow responses during the cognitive tasks, after normalizing for changes in arterial pressure. DC consumption also increased brachial FMD compared with the baseline value before chocolate consumption ( = 0.002), whereas MC and white chocolate (0% cocoa) caused no change (interaction between conditions = 0.034). Consumption of chocolate containing high concentrations of cocoa enhanced vascular endothelial function, which was reflected by improvements in FMD. Cognitive function outcomes did not differ between conditions; however, cerebral blood flow responses during these cognitive tasks were lower in those consuming MC and DC. These findings suggest that chocolate containing high concentrations of cocoa may modify the relation between cerebral metabolism and blood flow responses in postmenopausal women. This trial was registered at www.ANZCTR.orgau as ACTRN12616000990426.

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Purpose We studied individual variability in exercise responses in twins. We hypothesized that 1) endurance (END) training would reduce fat mass whereas resistance (RES) training would increase lean mass, 2) individuals who did not respond to one modality would respond to the other, and 3) cross-sectional heritability estimates would be higher than estimates based on training responses. Methods DXA was undertaken in 84 same-sex untrained twins (30 monozygotic [MZ], 12 dizygotic [DZ]). Participants underwent 3 months of END and RES training, separated by 3 months washout. Twins trained in pairs. Results RES (P < 0.001) and END (P = 0.002) increased lean mass, with a greater change in RES (P < 0.001). Similarly, RES (P = 0.04) and END (P = 0.006) decreased fat mass. Eighty-four percent of subjects responded positively to RES for lean mass and 58% to END (P < 0.001). For fat mass, RES and END induced 56% and 66% responder rates, respectively (P = 0.28). Cross-sectional intraclass correlations, used to assess the similarity in twin responses, were higher for MZ than DZ pairs for all variables. Following training, only MZ pairs were significantly correlated (P < 0.001) for change in lean mass to RES. Conclusion To our knowledge, this study is the first to report individual responsiveness in body composition to both RES and END in the same subjects. Although RES and END induced favorable changes in fat mass, RES was superior for lean mass. The frequency of lean mass responders to RES exceeded that for END, whereas response rates for fat mass were similar. Cross-sectional heritability estimates were higher than training response estimates, and shared environment had the largest influence on changes in body composition. This study suggests that exercise professionals should consider modality and environmental factors when optimizing exercise interventions.