Resistance Exercise and Glycemic Health: Investigating the Impact of Resistance Exercise in Healthy Individuals and Those with Impaired Glucose Homeostasis

Abstract

Resistance exercise (RE) is a powerful exercise modality used across the lifespan to promote healthy skeletal muscle mass. While most engage in RE to improve strength, size, and physical functionality, there are metabolic advantages for maintaining healthy levels of skeletal muscle because it is the primary storage site of glucose. Understanding this, RE may be important, especially in individuals with impaired glucose homeostasis. While we have clear evidence that RE improves glycemic outcomes in individuals with impaired glucose homeostasis it is unclear to what degree shifts in lean mass (LM) moderate these changes. Understanding how shifts in LM as well as RE prescription features leading to improved glycemic outcomes may better inform health practitioners working with this population. In contrast, in younger, athletic individuals, RE is commonly used in conjunction with a caloric surplus, to intentionally gain body mass to improve sports performance, improve aesthetics, or improve occupational performance in populations such as military personnel. However, the metabolic implications of this practice are largely unresearched. The objectives of this dissertation are to determine: (1) the effects of intentional weight gain with RE on fasting blood glucose (FBG), 24-hr mean glucose, and glycemic variability using continuous glucose monitoring (CGM) in younger athletic individuals and (2) the effects of RE-induced lean mass in populations at risk of or with type 2 diabetes To assess how CGM has been utilized in conjunction with RE in normoglycemic individuals a narrative review was conducted. The search located 3 clinical trials and 2 observational trials. Based on the observed literature there is currently not a justification for the use of CGM in conjunction with CGM to enhance RE outcomes or glycemic health. In addition, the available studies evaluated acute glycemic responses to RE rather than assessing chronic adaptations after a period of training. This presents a gap in literature that warrants future research. In conjunction with a larger trial investigating weight gain in athletic individuals we determined the effects of intentional weight gain on glycemic health utilizing CGM-derived indices of glycemic health and fasting blood glucose (FBG). Thirty-two athletic individuals were randomized to a peanut containing snack group (PNT) or a higher carbohydrate containing snack group (CHO), each designed to provide participants with an additional 500 kcal/day. Participants also engaged in a whole-body hypertrophy-focused RE protocol 3 days/week for 10 weeks. CGM devices were worn for a 3-day wear period before the intervention and during week 10. Dual-energy X-ray absorptiometry was used to measure body composition pre- and post- intervention. Linear mixed effects models were used to evaluate how changes in body composition affect glycemia. The final analysis included 26 individuals (46% female) aged 24 ± 6 years, with a BMI of 23 ± 3 kg/m². Total weight gain was different between snack groups (PNT: 1.49 ± 1.18 kg, CHO: 2.88 ± 1.18 kg; p= 0.006) and fat mass (FM) gain was higher in CHO (0.98 ± 0.82 kg) compared to PNT (0.50 ± 0.40 kg) (p=0.016). There were no group differences in LM gain (PNT: 1.26 ± 1.06 kg, CHO: 1.90 ± 1.01kg; p= 0.133). There were no group differences in CGM-derived indices of glycemia or FBG. FBG tended to increase with FMI (β=2.32; 95%CI: 0.06, 4.58; p= 0.045). Lean mass index (LMI) was associated with increased time in range (TIR) (β= 2.46; 95%CI: 0.46, 4.45; p= 0.018) as well as mean glucose (meanG) (β= 2.52; 95%CI: 1.32, 3.71; p< 0.001). MeanG had a three-way interaction for group, LMI, and FMI (β= 1.68; 95%CI: 0.18, 3.18; p= 0.031) and LMI, FMI, time (β= 1.35; 95%CI: 0.01, 2.70; p= 0.049). CGM-derived indices of glycemic health did not change after 10 weeks of intentional weight gain via resistance exercise and energy surplus in athletic, normoglycemic individuals. LMI and FMI are associated with shifts in CGM-derived indices of glycemic health and may be linked in their influence on certain measures such as meanG. Additional research is needed to expand this potential relationship to determine how body composition may influence CGM-derived measures of glycemic health. To determine if RE-induced gains in LM effects glucose homeostasis in individuals with impaired glycemic control we conducted a systematic review. We observed a mean gain in LM was ≥ 2kg was associated with the largest decrease in HBA1c. Additionally, the RE prescription that appeared to be most effective in improving HBA1c utilized ≥ 9 sets per muscle group/exercise/week of ~60%1RM or more, for ≥ 8 repetitions, and a duration of 12-26 weeks.