Examination of Sex-Specific Participant Inclusion in Exercise Physiology Endothelial Function Research: A Systematic Review

Abstract

BackgroundTo combat historical underrepresentation of female participants in research, guidelines have been established to motivate equal participation by both sexes. However, the pervasiveness of female exclusion has not been examined in vascular exercise physiology research. The purpose of this study was to systematically quantify the sex-specific prevalence of human participants and identify the rationales for sex-specific inclusion/exclusion in research examining the impact of exercise on vascular endothelial function.MethodsA systematic search was conducted examining exercise/physical activity and vascular endothelial function, assessed via flow mediated dilation. Studies were categorized by sex: male-only, female-only, or mixed sex, including examination of the sample size of males and females. Analysis was performed examining sex-inclusion criteria in study design and reporting and rationale for inclusion/exclusion of participants on the basis of sex. Changes in proportion of female participants included in studies were examined over time in 5 year cohorts.ResultsA total of 514 studies were identified, spanning 26 years (1996–2021). Of the total participants, 64% were male and 36% were female, and a male bias was identified (32% male-only vs. 12% female-only studies). Proportions of female participants in studies remained relatively constant in the last 20 years. Male-only studies were less likely to report sex in the title compared to female-only studies (27 vs. 78%, p < 0.001), report sex in the abstract (72 vs. 98%, p < 0.001) and justify exclusion on the basis of sex (15 vs. 55%, p < 0.001). Further, male-only studies were more likely to be conducted in healthy populations compared to female-only studies (p = 0.002). Qualitative analysis of justifications identified four themes: sex-specific rationale or gap in the literature, exclusion of females based on the hormonal cycle or sex-differences, maintaining congruence with the male norm, and challenges with recruitment, retention and resources.ConclusionsThis systematic review provides the first analysis of sex-based inclusion/exclusion and rationale for sex-based decisions in human vascular exercise physiology research. These findings contribute to identifying the impact of research guidelines regarding inclusion of males and females and the perceived barriers to designing studies with equal sex participation, in an effort to increase female representation in vascular exercise physiology research.Systematic Review Registration:CRD42022300388.

Exercise training reduces arterial stiffness in women with high blood pressure: a systematic review and meta-analysis

“…Only small decreases in PWV were observed following resistance training interventions. The findings here also highlight that relatively sparse number of robust trials (RCTs) examining the influence of exercise on arterial stiffness in women, which supports the consensus that data on women is limited across many domains in exercise science [27,31,32]. Notably, no RCTs have analyzed the influence of concurrent training (aerobic exercise plus resistance exercise training) on PWV in women with high blood pressure.…”

“…It was, however, restricted to RCTs investigating the influence of exercise on PWV and in patients with prehypertension/hypertension, focusing on postmenopausal women, which is a strength of the work. It was not particularly unexpected to only find six eligible studies for inclusion in this review when the pervasive sex bias in exercise science and sports medicine research was noted a priori [27,31,32]. Nonetheless, this systematic review and meta-analysis presents important data on the benefits of aerobic and resistance training for improving arterial health in women with high blood pressure and offers practical advice for exercise professionals.…”

“…The sex bias in exercise science and sports medicine research remains an important issue, despite significant progress made for women in sport since the middle of the 20th century. A recent systematic review emphasized the lack of female-only studies and disaggregated data focusing on women in published work examining the impact of exercise training and physical activity on vascular endothelial function [27]. Considerable biological and physiological differences are observed between men and women before and after menopause.…”

Current evidence shows no influence of women's menstrual cycle phase on acute strength performance or adaptations to resistance exercise training

“…Premenopausal women are frequently excluded from exercise physiology research to avoid the potential influence of varying ovarian hormones across the menstrual cycle. This assumption perpetuates a widespread sex-based bias in the exercise physiology literature ( 4 , 36 ), despite profound interindividual variability in the magnitude of hypertrophic response to RET in both women and men ( 37 , 38 ). Further, we note that detailed comparisons of men and women in their propensity for RET-induced hypertrophy indicate equivalent relative gains in muscle size and, for the most part, strength ( 39 ).…”

Moderate to Vigorous-intensity Continuous Training versus Highintensity Interval Training for Improving VO2max in Women: A Systematic Review and Meta-analysis

“…The sex bias in research trials examining the influence of exercise on cell-free DNA was recently highlighted [23]. Although cell-free DNA is an emerging biomarker not traditionally used in clinical or athletic domains, others have demonstrated a similar sex bias in other exercise science topics (e. g. human vascular exercise physiology) [24]. Therefore, examples of female-only studies seem to be the exception, not the rule.…”