Necessity of Considering Sex of Participants in Research: Observations Drawn From Resistance Training Studies of Older Adults

in Journal of Aging and Physical Activity
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  • 1 Faculty of Health and Social Development, Healthy Exercise and Aging Laboratory, Aging In Place Research Cluster, School of Health and Exercise Sciences, The University of British Columbia, Okanagan Campus, Kelowna, BC, Canada

Adult aging is a natural and complex phenomenon that is ostensibly alike between men and women. Generally, women live longer than men, yet women are frailer and have worse health at the end of life; the male–female health-survival paradox. What remains even more baffling than the potential paradox between longevity and function in men and women, is the paucity of research on sex- and gender-specific differences to exercise, particularly in response to strength training which is known to benefit functional ability (Brady et al., 2014; Brandon et al., 2004; Papiol et al., 2016) and mitigate frailty (Watanabe et al., 2013). Although exercise and physical activity cannot independently alter the health piece of the paradox, notably that associated with disease, the female disadvantages in health and function have the potential to be quelled with strength training. Research published in the Journal of Aging and Physical Activity shows hope; yet, more studies are needed.

Although the designation of male and female (biological study factors) and men and women (psychosocial study factors) is outlined for scientific research (see Sex and Gender Equity in Research Guidelines, National Institute of Health, and Canadian Institute of Health Research Resources), and evidence is accumulating across disciplines that various types of interventions (e.g., pharmaceuticals responses toward pain) have sex-specific (male and female) and gender-specific (men and women) outcomes, research and reporting on sex- and gender-specific responses to exercise and physical activity is scarce. Publications, across the history (1993—Vol. 29, Issue 4, 2021) of Journal of Aging and Physical Activity were examined for strength training, gender (women and men), and sex (females and males) in older adults. The concentrated initial search of this journal through the PubMed database (https://pubmed.ncbi.nlm.nih.gov/) identified few (<10) studies that examined sex/gender as an independent variable with resistance training. Resultingly, sex-related search terms were removed and papers that applied strength/resistance training interventions were evaluated for inclusion of both sexes/genders within the abstract, keywords, and title; and this resulted in 75 studies. Subsequent inspection of these primary papers prompted the exclusion of 44 studies because methodologically sex was not delineated as an independent variable (e.g., independent data not reported for males and females, participants statistically collapsed). This approach to research reporting, potentially arising from low statistical power or nonsignificant group differences need to discontinue. Current dogma is that to enhance reproducibility, advance knowledge of adult aging, and for this journal identify the benefit of exercise/physical activity, researchers should address and report relevant biological (sex) and sociological (gender) variables, beyond subject characteristics and statistical significance. Of the remaining 31 studies, 16 were eventually selected for inclusion based upon reporting sex-related differences in physical function and muscle strength (n = 7) and strength training interventions in older females and males (n = 9) (Table 1).

Table 1

Sex-Based Studies

StudyStudy typeInterventionSex-based differences (Y/N)Sex-based differences: Explanation
Brandon et al. (2014)PrimaryStrength and flexibility training, two to three times per week for 96 weeks, 11 exercises, three sets of eight to 12 repetitions per exercise (60-min session)N

M = F
No differences between males and females
Costa et al. (2018)PrimaryResistance training three times per week for 12 weeks, two to three sets of eight to 12 repetitionsNNo comparison as the subjects were all females
Daly et al. (2013)PrimaryResistance training three times per week for 6 weeks, nine exercises, three sets of eight repetitionsY

M > F
Elbow flexor and wrist extensor muscle volume and elbow extension force are greater in males than females
Giné-Garriga et al. (2010)PrimaryStrength training two times per week for 12 weeks, one to two sets of six to 15 repetitions per exercise (45-min session)Y

F > M
Maximal force declined in females but not males 24 weeks after completion of a training program
Herda et al. (2021)PrimaryResistance training three times per week for 12 weeks, three exercises, three sets of eight to 12 repetitions per exerciseNNo differences between males and females
Herrema et al. (2018)PrimaryStrength training two times per week for 12 weeks (90-min session)NNo differences between males and females (qualitative interview)
Lohne-Seiler et al. (2013)PrimaryStrength training two times per week for 11 weeks, three sets of six to 10 repetitions per exercise (70-min session)Y

M > F
Improvement in bench press force in males but not females following high-power strength training
Marsh et al. (2009)PrimaryResistance training three times per week for 12 weeks, three sets of eight to 10 repetitions per exerciseY

F < M

CS
Females less likely to CS
Watanabe et al. (2013)PrimaryResistance training two times per week for 12 weeks, two exercises, three sets of eight repetitions per exerciseNNo differences between males and females
Brady et al. (2014)PrimaryNo training interventionY

F < M

Disability

M > F PF
Females have greater rates of disability and lower PF than males
Fell and Williams (2008)ReviewNo training interventionY

F > M
Higher levels of muscle damage in females than males
Galvão et al. (2005)ReviewNo training interventionY

M > F
Males generally stronger than females
Gouveia et al. (2013)PrimaryNo training interventionY

M > F strength

M < F flexibility
Males perform better on strength-based movements, whereas females perform better in flexibility-based movements
Lopez et al. (2017)Meta-analysisNo training interventionNNo difference between males and females
Papiol et al. (2016)PrimaryNo training interventionY

M < F
Reduced prevalence of frailty in males than females
Stegink Jansen et al. (2008)PrimaryNo training interventionY

M > F
Male display greater grip force strength than females

Note. The top section of the table includes studies that included strength training interventions. M = males; F = females; Y = yes; N = no; PF = physical function; CS = complete study.

Highlights From Papers Within Virtual Special Issue

The citations and full text from the Journal of Aging and Physical Activity are included in the virtual special issue.1 Citations and references outside of this journal are identified in the reference list. Community-dwelling older males tend to perform better on functional tasks, such as the 6-min walk, 8-feet up-and-go, and chair stands than female subjects (Gouveia et al., 2013), and are at lesser risk of frailty (Costa et al., 2020). Frailty, which increases susceptibility to stressors with advanced age (Papiol et al., 2016), is associated with a significant loss of strength and function. Markedly, and although not significant Papiol et al. (2016) reported that loss of strength was associated with ~58% of females diagnosed with frailty and 43% of males (p = .11). Strength training has shown strong potential to prevent, mitigate, and even reverse the process of frailty (Giné-Garriga et al., 2010; Lopez et al., 2018); and although exercise studies have been directed toward females (Costa et al., 2020), more studies are required to understand aged female-specific responses to strength training.

Although strength training effects are often assumed to be universal between the sexes, the literature is equivocal. One difficulty in understanding adaptations and the underlying factors is the majority of studies published only evaluated sex as a secondary measure, if at all, and not a priori (Marsh et al., 2009). In their narrative literature review, Galvao et al. (2005) indicate that strength training induces positive changes in muscle size, and in this report the authors identified that there were similar anabolic responses between males and females; however, they also stated that sample size across the intervention studies were relatively small to detect significant sex differences. Other studies have observed greater changes in males compared with females following resistance training. For example, males compared with females following 9 weeks of resistance training had a greater increase in thigh muscle volume (Ivey et al., 2000), and after 24 weeks of high-load and power training Type I, IIa, and IIb muscle fiber cross-sectional area of the vastus lateralis increased by ~48% in males, whereas females increased ~27% (Hakkinen et al., 2002). The greater response in males following training has been observed in upper (Lohne-Seiler et al., 2013) and lower limbs (Giné-Garriga et al., 2010), albeit not with high statistical power.

Contrary to evidence that suggests sex-specific hypertrophic-like muscle and force changes in responses to resistance training, there are also reports which suggest females and males respond similarly. When older adult females and males train and are allowed to self-select exercise type and intensity (Herda et al., 2021), or given a low-intensity strength training program (Watanabe et al., 2013), similar improvements in muscle size, force, and functional mobility occur between sexes. The difference in sex-specific outcomes suggests that intensity and type of training employed in the intervention is critical, and potentially “coaching” for older adults might be an important motivator (Herrema et al., 2018) and this requires dedicated intervention studies in older females and males. It is time to pay heed to published observations, and statements, within this journal indicating that more detailed between-sex examination is an important focus of future research (Lohne-Seiler et al., 2013). Muscle weakness is a key component of functional decline (Brady et al., 2014), and in order to understand the potential for strength training to yield a sex-specific response and establish the effectiveness of exercise programs for males and females from small cohort studies sex/gender need to be delineated (Daly et al., 2013; Galvão et al., 2005) and larger cohort studies undertaken.

Alongside beneficial effects, strength training can induce significant damage to skeletal muscle. Fell and Williams (2008), in their literature review, reported that Roth et al. (2000) demonstrated increased muscle damage with aging in females, with no differences in males, and suggested that these responses may stem from dissimilar adaptations to similar training interventions between sexes (Fell & Williams, 2008). Greater research is needed to understand sex-based difference in skeletal muscle damage to exercise training, and this extends to understanding detraining. Subsequent to a 12-week intervention, males maintained strength gains to a greater degree than females over the 24-week postintervention (Giné-Garriga et al., 2010). These sex-specific observations are contrary to those of Ivey et al. (2005); reported in Galvao et al. (2005) in that a more rapid loss of muscle mass was observed in males compared with females following a 31-week detraining period. This acute period of decline, being greater in males compared with females, aligns with the observed losses in force production over several decades being greater in males than females for handgrip (Stegink Jansen et al., 2008). Although males compared with females are typically stronger (Stegink Jansen et al., 2008) and thereby have a greater force reserve to meet key strength thresholds required for activities of daily living (Galvão et al., 2005), the rate of strength loss in an acute period following training, as well as long-term, is not well-understood and longitudinal comparative studies between sexes, although challenging, would be ideal.

There is a paramount need to further our understanding of the physiological factors that are contributing to, or not, the positive influence of strength training in older adults. Although more research is needed on older females and understanding sex-specific differences in response to strength training and detraining, consideration of studies within Journal of Aging and Physical Activity portray high optimism to advancing an understanding of sex-specific exercise interventions for older adults. The Journal of Aging and Physical Activity through Associate Editors meeting have initiated discussions and processes to instruct authors and reviewers on the research design and reporting principles surrounding sex and gender in research (Heidari et al., 2016); progressive change will lend knowledge to the potential for physical activity to reduce the male–female health-survival paradox.

Note

1.

The JAPA papers cited in-text are included in the virtual special issue.

References

  • Hakkinen, K., Kraemer, W.J., Pakarinen, A., Triplett-McBride, T., McBride, J.M., Hakkinen, A., Alen, M., McGuigan, M.R., Bronks, R., & Newton, R.U. (2002). Effects of heavy resistance/power training on maximal stregnth, muscle morphology, and hormonal response patterns in 60–75-year-old men and women. Canadian Journal of Applied Physiology, 27(3), 213231. https://doi.org/10.1139/h02-013

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  • Heidari, S., Babor, T.F., De Castro, P., Tort, S., & Curno, M. (2016). Sex and gender equity in research: Rationale for the SAGER guidelines and recommended use. Research Integrity and Peer Review, 1(1), 19. https://doi.org/10.1186/s41073-016-0007-6

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  • Ivey, F.M., Hurley, B.F., Roth, S.M., Ferrell, R.E., Tracy, B.L., Lemmer, J.T., Hurlbut, D.E., Martel, G.F., Siegel, E.L., Fozard, J.L., Jeffrey Metter, E., Fleg, J.L., & Hurley, B.F. (2000). Effects of age, gender, and myostatin genotype on the hypertrophic response to heavy resistance strength training. The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences, 55(11), M641M648. https://doi.org/10.1093/gerona/55.11.M641

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  • Hakkinen, K., Kraemer, W.J., Pakarinen, A., Triplett-McBride, T., McBride, J.M., Hakkinen, A., Alen, M., McGuigan, M.R., Bronks, R., & Newton, R.U. (2002). Effects of heavy resistance/power training on maximal stregnth, muscle morphology, and hormonal response patterns in 60–75-year-old men and women. Canadian Journal of Applied Physiology, 27(3), 213231. https://doi.org/10.1139/h02-013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Heidari, S., Babor, T.F., De Castro, P., Tort, S., & Curno, M. (2016). Sex and gender equity in research: Rationale for the SAGER guidelines and recommended use. Research Integrity and Peer Review, 1(1), 19. https://doi.org/10.1186/s41073-016-0007-6

    • Search Google Scholar
    • Export Citation
  • Ivey, F.M., Hurley, B.F., Roth, S.M., Ferrell, R.E., Tracy, B.L., Lemmer, J.T., Hurlbut, D.E., Martel, G.F., Siegel, E.L., Fozard, J.L., Jeffrey Metter, E., Fleg, J.L., & Hurley, B.F. (2000). Effects of age, gender, and myostatin genotype on the hypertrophic response to heavy resistance strength training. The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences, 55(11), M641M648. https://doi.org/10.1093/gerona/55.11.M641

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    • Export Citation
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