The Effect of Exercise on Cardiometabolic Parameters in Women with Insulin Resistance

I chose to critique a journal article from the Journal of Applied Physiology, which discussed the results of a randomized clinical trial conducted to study the effects of exercise training on several glucose control variables in obese women with insulin resistance (Álvarez, Ramírez-Campillo, Ramírez-Vélez, & Izquierdo, 2017). This critique includes a summary of the research article followed by an evaluation of the study and its relevance to researchers and practitioners of exercise physiology.

According to the authors, moderate to vigorous exercise training regimens can provide therapeutic support, or even prevention, in the pre-diagnosis stage of type 2 diabetes mellitus (T2DM) when insulin resistance develops. For example, in previous studies, even two weeks of high-intensity interval training (HIIT) has been shown to decrease blood glucose concentration and increase endurance performance. However, due to interindividual variability, some patients benefit from the positive effects of exercise training, whereas others experience worsened or no response. Because of genetic and environmental factors, these nonresponders (NRs) may have higher risk factors for morbidity and mortality related to T2DM. The authors highlighted the need for additional research on environmental influences that may affect NR, including different modes of exercise training and health factors.

The purpose of the study was to determine the effects of two modes of exercise training on NR prevalence as well as anthropometric, cardiovascular, strength, and endurance measures in sedentary obese women with insulin-resistant T2DM. The prevalence of NR was defined as the percentage of nonresponders following a training intervention. Patients from a family healthcare center in Chile were eligible to participate in the study if they 1) were female, 2) had a body mass index (BMI) between 25 and 35 kg/m2, 3) were diagnosed as having insulin resistance between 1 and 3 months, 4) were physically inactive as assessed by the International Physical Activity Questionnaire, 5) had no involvement in a physical activity program for the previous 6 months, 6) and had no family history of T2DM. Participants were randomly assigned to one of two treatment groups, participating in either 12 weeks of HIIT or resistance training (RT) during supervised triweekly exercise sessions. Anthropometric, cardiovascular, strength, and endurance measures were assessed in both treatment groups before the exercise intervention and at a 12-week follow up. The results indicated that the HIIT and RT programs both effectively reduced fasting glucose, fasting insulin, and systolic blood pressure (BP). Following the intervention, there were no differences in NR prevalence when comparing the HIIT and RT programs.

My critique of the article revealed a comprehensive and valuable research study. However, a few lingering questions remain related to the sample, research design, and clinical significance of the results. The introduction summarized previous studies related to the effects of various forms of exercise training on glucose control variables, strength performance, and the prevalence of NR in participants with T2DM. Although the research review made a strong case for comparing different modes of exercise training on cardiometabolic health variables, the authors did not explain their purpose for recruiting only women for this study. The reason for this decision would be important for possible treatment recommendations for practitioners in physical education, human performance, and medicine.

An additional possible omission relates to the traditional components of a quantitative research report. After setting up the rationale and purpose for the study, the authors do not state their research questions. Nor do they state hypotheses as predictions about the outcome of the study. Making a prediction about the outcome(s) of the experiment lends credibility to the knowledge and expertise of the researchers. Without the research questions and hypotheses, the results seem a bit disconnected from the prior research included in the introduction. Although the research questions and hypotheses feel as if they are missing, the discussion section integrates the results of the current study into those of prior research.

As a novice reader of exercise physiology research, it is difficult to determine whether the “statistically significant” differences in anthropometric, cardiovascular or muscle performance measures from pre-assessment to post-assessment are also clinically significant. For example, the authors state that the “systolic BP was decreased after both programs by -4.5% in HIIT and -3.1% in RT as well as heart rate at rest by -3.6% in HIIT group” (Álvarez et al., 2017, p. 994). If I could ask the authors a few questions, I would ask, “Are these percent decreases clinically significant? Are the changes big enough to make the exercise programs worthwhile?”

Despite some remaining questions, the results of this study have valuable implications for exercise physiology, especially related to the impact of physical activity on the cardiovascular, muscular, and endocrine systems of obese women with insulin resistance. Further, Álvarez et al. (2017) indicate that their participants achieved these results with a 24-28% lower weekly exercise time commitment than the current minimal American College of Sports Medicine and American Diabetes Association recommendations for people with T2DM. Although further research will most likely be needed to confirm these results, a reduced exercise commitment may be a critical factor for improving compliance and engagement with effective modes of exercise training.

Reference

Álvarez, C., Ramírez-Campillo, R., Ramírez-Vélez, R., & Izquierdo, M. (2017). Effects and prevalence of nonresponders after 12 weeks of high-intensity interval or resistance training in women with insulin resistance: A randomized trial. Journal of Applied Physiology, 122(4), 985-996. doi:10.1152/japplphysiol.01037.2016