Resistance Training as a Countermeasure in Women with Gestational Diabetes Mellitus: A Review of Current Literature and Future Directions.

Gestational diabetes mellitus (GDM) poses a significant health concern for both mother and offspring. Exercise has emerged as a cornerstone of glycemic management in GDM. However, most research regarding this topic examines aerobic training (AT), despite substantial evidence for the effectiveness of resistance training (RT) in improving dysregulated glucose in other groups of people with diabetes, such as in type 2 diabetes mellitus (T2DM). Thus, the purpose of this paper is to review research that examined the impact of RT on markers of glucose management in GDM, and to discuss future research directions to determine the benefits of RT in GDM. Based on the current evidence, RT is effective in reducing insulin requirement, especially in overweight women, reducing fasting glucose concentrations, and improving short-term postprandial glycemic control. However, the number of studies and findings limit conclusions about the impact of RT on risk of GDM, fasting insulin concentrations, insulin resistance, ß-cell function, and intra-exercise glucose management. Overall, current evidence is accumulating to suggest that RT is a promising non-pharmacological tool to regulate circulating glucose concentrations in women with GDM, and a potential alternative or supplement to AT.

Circulating long-chain acylcarnitine concentrations are not affected by exercise training in pregnant women with obesity.

The purpose of this study was to determine the effect of exercise during pregnancy in sedentary women with obesity on longitudinal changes in long-chain acylcarnitine (LC-AC) concentrations. We hypothesized that exercise training would significantly decrease circulating LC-ACs throughout gestation compared with a nonexercise control group. Pregnant women with obesity considered otherwise healthy [n = 80, means ± SD; body mass index (BMI): 36.9 ± 5.7 kg/m2] were randomized into an exercise (n = 40, aerobic/resistance 3 times/wk, ∼13th gestation week until birth) or a nonexercise control (n = 40) group. At gestation week 12.2 ± 0.5 and 36.0 ± 0.4, a submaximal exercise test was conducted, and indirect calorimetry was used to measure relative resting energy expenditure (REE), as well as respiratory exchange ratio (RER) at rest. Fasting blood samples were collected and analyzed for LC-AC concentrations. Fitness improved with prenatal exercise training; however, exercise training did not affect circulating LC-AC. When groups were collapsed, LC-ACs decreased during gestation (combined groups, P < 0.001), whereas REE (kcal/kg/day, P = 0.008) increased. However, average REE relative to fat-free mass (FFM) (kcal/kg FFM/day) and RER did not change. There was an inverse relationship between the change in RER and all LC-ACs (except C18:2) throughout gestation (C14: r = -0.26, P = 0.04; C16: r = -0.27, P = 0.03; C18:1: r = -0.28, P = 0.02). In summary, a moderate-intensity exercise intervention during pregnancy in women with obesity did not alter LC-ACs concentrations versus control, indicating that the balance between long-chain fatty acid availability and oxidation neither improved nor worsened with an exercise intervention.NEW & NOTEWORTHY This research showed that a moderate-intensity prenatal exercise program, consisting of aerobic and resistance training, did not negatively impact normal alterations in substrate supply and demand for the mother and the offspring throughout gestation. Findings provide support for metabolic safety of exercise during pregnancy.

Markers of branched-chain amino acid catabolism are not affected by exercise training in pregnant women with obesity.

Despite the role of branched-chain amino acids (BCAAs) in physiological processes such as nutrient signaling and protein synthesis, there is ongoing debate about the link between circulating BCAAs and insulin resistance (IR) in various populations. In healthy women, IR mildly increases during pregnancy, whereas both BCAAs and markers of BCAA catabolism decrease, indicating that fetal growth is being prioritized. Exercise reduces IR in nonpregnant adults, but less is known about the effect of exercise during pregnancy in women with obesity on IR and BCAA breakdown. The aim of this study was to determine the effect of a moderate-intensity exercise intervention during pregnancy on maternal circulating BCAAs and markers of BCAA catabolism [short-chain acylcarnitines (ACs)], and their associations with IR. Healthy obese [n = 80, means ± SD; body mass index (BMI): 36.9 ± 5.7 kg/m2] pregnant women were randomized into an exercise (n = 40, aerobic/resistance 3×/wk, ∼13th gestation week until birth) or a nonexercise control (n = 40) group. Blood was collected at 12.2 ± 0.5 and 36.0 ± 0.4 gestation weeks and analyzed for BCAA-derived acylcarnitine concentrations as markers of BCAA breakdown toward oxidative pathways, and glucose and insulin concentrations [updated homeostatic model assessment of IR (HOMA2-IR)]. After adjusting for HOMA2-IR, there were no interaction effects of group by time. In addition, there was a main positive effect of time on HOMA2-IR (12 wk: 2.3 ± 0.2, 36 wk: 3.0 ± 0.2, P = 0.003). A moderate-intensity exercise intervention during pregnancy in women with obesity was not associated with changes in BCAA-derived ACs versus standard of care. The decrease in BCAA-derived ACs throughout gestation could not be explained by IR.NEW & NOTEWORTHY This research showed an increase in insulin resistance (IR) and decrease in branched-chain amino acid catabolism throughout gestation in women with obesity, and addition of a moderate exercise intervention (known to attenuate IR in nonpregnant populations) did not alter these shifts. Findings provide support for metabolic safety of exercise during pregnancy.

Dietary Protein Intake during Pregnancy Is Not Associated with Offspring Insulin Sensitivity during the First Two Years of Life.

Literature describing a relationship between dietary protein intake during pregnancy and offspring insulin resistance are equivocal perhaps because of the lapse between maternal and offspring measurements (~9-40 years). Thus, we evaluated protein intake in healthy women [n = 182, mean ± SD; body mass index (BMI): 26.2 ± 4.2 kg/m2] in early pregnancy (8.4 ± 1.6 weeks, EP), late pregnancy (30.1 ± 0.4 weeks, LP), and averaged throughout pregnancy, and determined the relationship between protein intake and offspring homeostatic model assessment of insulin resistance (HOMA2-IR) at 12 (12mo) and 24 (24mo) months. EP protein (g·kg-1·day-1) did not associate with HOMA2-IR at 12mo (ß = 0.153, p = 0.429) or 24mo (ß = -0.349, p = 0.098). LP protein did not associate with HOMA2-IR at 12mo (ß = 0.023, p = 0.916) or 24mo (ß = -0.442, p = 0.085). Finally, average protein did not associate with HOMA2-IR at 12mo (ß = 0.711, p = 0.05) or 24mo (ß = -0.445, p = 0.294). Results remained unchanged after adjusting for plant protein intake quartiles during pregnancy, maternal BMI, and offspring sex and body fat percentage. Additionally, these relationships did not change after quartile analysis of average protein intake, even after considering offspring fasting time and HOMA2-IR outliers, and maternal under-reporters of energy intake. Protein intake during pregnancy is not associated with indirect measurements of insulin sensitivity in offspring during the first two years of life.

Divergent Changes in Serum Branched-Chain Amino Acid Concentrations and Estimates of Insulin Resistance throughout Gestation in Healthy Women.

BACKGROUND: Branched-chain amino acid (BCAA) concentrations in the blood have been correlated with insulin resistance, but this relation throughout gestation (period in which insulin resistance typically increases) is unclear. OBJECTIVE: The objective of this study was to determine the associations between changes in BCAA concentrations and estimates of insulin resistance throughout gestation. METHODS: Serum BCAA (Leu, Ile, Val) concentrations and insulin resistance/sensitivity [i.e., homeostatic model assessment-2 of insulin resistance (HOMA2-IR), estimated metabolic clearance rate (MCR) of glucose, and estimated first- and second-phase insulin responses] were assessed at early (EP; 8.5 ± 0.2 wk) and/or late (LP; 29.2 ± 0.8 wk) pregnancy in 53 healthy women from the Glowing cohort. Adjusted Spearman correlations were used to evaluate the association between BCAA and insulin resistance/sensitivity measures at EP and LP, adjusted for body fat percentage and gestational weight gain (GWG). A multiple linear regression analysis was used to assess the association between changes in HOMA2-IR and BCAAs throughout gestation. Groups were made post hoc based on the mean percentage change (10% decrease) in Leu throughout gestation, creating a group with a ≥10% decrease in LeuLP-EP (BELOW) and a <10% decrease in LeuLP-EP (ABOVE), and Student's t tests were performed to assess differences between groups. RESULTS: Leu and Ile concentrations positively correlated with HOMA2-IR at both time points, but these relations at EP disappeared/weakened when adjusted for body fat percentage. From EP to LP, the change in Leu (LeuLP-EP) was negatively associated with the change in HOMA2-IR (HOMA2-IRLP-EP) (ß = -0.037, P = 0.006). MCR was lower in the BELOW group compared with the ABOVE group, whereas there was no difference in HOMA2-IR between groups. CONCLUSIONS: In this pregnancy cohort, BCAA concentrations decreased throughout gestation, whereas the mean insulin resistance did not change. These data do not support a connection between changes in blood BCAA concentrations and estimates of insulin resistance in pregnant women. This trial is registered at clinicaltrials.gov as NCT01131117.

Lipolysis and Fat Oxidation Are Not Altered with Presleep Compared with Daytime Casein Protein Intake in Resistance-Trained Women.

BACKGROUND: To date, no studies have directly compared the differences between presleep and daytime protein (PRO) consumption on localized and systemic fat metabolism in active women. OBJECTIVE: The purpose of this study was to assess the effects of presleep compared with daytime PRO supplementation on subcutaneous abdominal adipose tissue (SCAAT) lipolysis and whole-body substrate utilization in women. METHODS: Thirteen young (mean ± SE age: 22 ± 1 y; BMI: 24.3 ± 0.8 kg/m2), resistance-trained [1 repetition maximum (1RM) squat percentage of body weight: 135% ± 6%; 1RM bench press percentage of body weight: 82% ± 4%] women volunteered. On overnight experimental visits, participants performed full-body resistance exercise (RE; 65% 1RM) and were randomly assigned to consume either daytime PRO (PRO, 30 g casein) 30 min post-RE and presleep (30 min before bed) noncaloric, sensory-matched placebo (PLA, 0 g casein) (PRO-PLA), or the opposite (PLA-PRO), switching the order of the supplements on the following visit. SCAAT lipolysis, resting metabolism (indirect calorimetry), and plasma biomarkers (glucose, insulin, nonesterified fatty acids, glycerol) were measured at baseline, overnight, and the next morning. RESULTS: There were no differences in overnight SCAAT lipolysis between conditions indicated by interstitial glycerol concentrations (PRO-PLA: baseline, 669 ± 137; next morning, 321 ± 77.1; PLA-PRO: baseline, 524 ± 109; next morning, 333 ± 68.0 µM), fat oxidation (PRO-PLA: baseline, 5.70 ± 0.35; next morning, 5.00 ± 0.28; PLA-PRO: baseline, 6.59 ± 0.32; next morning, 5.44 ± 0.27 g/min), or any other measure. CONCLUSIONS: There was no difference between the effects of daytime and presleep PRO supplementation on SCAAT lipolysis or whole-body substrate utilization in resistance-trained women. Presleep PRO is a viable option for increasing PRO consumption in resistance-trained women because it does not blunt overnight lipolysis, and will therefore likely not lead to increases in subcutaneous abdominal fat.This trial was registered at clinicaltrials.gov as NCT03573687.

Obesity Status Affects the Relationship Between Protein Intake and Insulin Sensitivity in Late Pregnancy.

The purpose of this study was to determine the associations between amount and type of dietary protein intake and insulin sensitivity in late pregnancy, in normal weight and overweight women (29.8 ± 0.2 weeks gestation, n = 173). A 100-gram oral glucose tolerance test (OGTT) was administered following an overnight fast to estimate the metabolic clearance rate of glucose (MCR, mg · kg-1 · min-1) using four different equations accounting for the availability of blood samples. Total (TP), animal (AP), and plant (PP) protein intakes were assessed using a 3-day food record. Two linear models with MCR as the response variable were fitted to the data to estimate the relationship of protein intake to insulin sensitivity either unadjusted or adjusted for early pregnancy body mass index (BMI) because of the potential of BMI to influence this relationship. There was a positive association between TP (ß = 1.37, p = 0.002) and PP (ß = 4.44, p < 0.001) intake in the last trimester of pregnancy and insulin sensitivity that weakened when accounting for early pregnancy BMI. However, there was no relationship between AP intake and insulin sensitivity (ß = 0.95, p = 0.08). Therefore, early pregnancy BMI may be a better predictor of insulin sensitivity than dietary protein intake in late pregnancy.

The Association of Maternal Protein Intake during Pregnancy in Humans with Maternal and Offspring Insulin Sensitivity Measures.

The purpose of this review is to critically evaluate the studies assessing the relations between protein intake during human pregnancy and insulin sensitivity measures in the mother and offspring, and to get a better understanding of the knowledge gaps that still exist. Overall, there is insufficient evidence to conclude about implications of higher amounts of protein intake during pregnancy on maternal or offspring insulin sensitivity. However, studies show a relation between protein quality and insulin sensitivity, such that animal protein may be associated with negative outcomes and plant protein may be associated with positive insulin sensitivity outcomes. There is an urgent need for standardized studies using comparable terminology to evaluate any potential relations between insulin sensitivity in mothers and offspring and truly low and high maternal protein intake while maintaining eucaloric balance to better inform about optimal protein dosage and quality during this period.

Fat metabolism and acute resistance exercise in trained women.

This study investigated the effect of acute full-body resistance exercise [RE; one set of 10 repetitions at 40% 1 repetition maximum (1RM) and three sets of 10 repetitions at 65% 1RM] on subcutaneous abdominal adipose tissue (SCAAT) lipolysis and whole body substrate oxidation in young (age: 22 ± 1 yr), normal-weight and body fatness (body mass index: 20 ± 1 kg/m2; %body fat: 28.7 ± 1.4%), resistance-trained women. Microdialysis was used to measure SCAAT lipolysis at baseline, mid-RE, post-RE, and 30 min post-RE, and indirect calorimetry was used to measure whole body substrate oxidation at baseline and immediately post-RE in 13 women. Plasma concentrations of glucose, insulin, nonesterified fatty acids (NEFA), glycerol, growth hormone (GH), epinephrine (Epi), and norepinephrine (NE) were measured at baseline, mid-RE, and post-RE. Lipolysis (dialysate glycerol concentration) was elevated post-RE (baseline: 596.7 ± 82.8, post-RE: 961.4 ± 116.3 µM, P = 0.01). Energy expenditure (baseline: 1,560 ± 49; post-RE: 1,756 ± 68 kcal/day; P = 0.02) and fat oxidation (baseline: 5.64 ± 0.24; post-RE: 7.57 ± 0.41 g/h; P = 0.0003) were elevated post-RE. GH (baseline: 513.1 ± 147.4; mid-RE: 1,288.3 ± 83.9; post-RE: 1,522.8 ± 51.1 pg/ml, P = 0.000), Epi (baseline: 23.2 ± 2.7; mid-RE: 92.5 ± 16.6; post-RE: 84.5 ± 21.4 pg/ml, P = 0.000), and NE (baseline: 139.2 ± 13.6; mid-RE: 850.9 ± 155.3; post-RE: 695.3 ± 93.5 pg/ml, P = 0.000) were higher at mid-RE and post-RE. Therefore, one of the potential mechanisms behind RE-induced fat mass changes in resistance-trained women may be in part due to the accumulated effect of transient increases in SCAAT lipolysis, fat oxidation, and energy expenditure, mediated by GH, Epi, and NE release.

Efficacy of the Repetitions in Reserve-Based Rating of Perceived Exertion for the Bench Press in Experienced and Novice Benchers.

Ormsbee, MJ, Carzoli, JP, Klemp, A, Allman, BR, Zourdos, MC, Kim, J-S, and Panton, LB. Efficacy of the repetitions in reserve-based rating of perceived exertion for the bench press in experienced and novice benchers. J Strength Cond Res 33(2): 337-345, 2019-Autoregulation (AR) is the practice of adjusting training variables in response to athlete feedback. One component of AR postulated to enhance resistance training adaptations involves implementing a resistance training-specific rating of perceived exertion (RPE) scale measuring repetitions in reserve (RIR). The purpose of this study was to examine the efficacy of this method using the bench press exercise. Twenty-seven college-aged men were assigned to one of 2 groups based on training age: experienced benchers (EB) (n = 14, training age: 4.7 ± 2.0 years) and novice benchers (NB) (n = 13, training age: 1.1 ± 0.6 years). Subjects performed 1 repetition maximum (1RM) followed by single-repetition sets with loads corresponding to 60, 75, and 90% of 1RM and an 8-repetition set at 70% of 1RM. Subjects reported a corresponding RPE, based on RIR, for every set. Average velocity was recorded for each single-repetition set along with the first and last repetitions of the 8-repetition set at 70% of 1RM. Average velocity at 100% of 1RM in EB was slower (0.14 ± 0.04 m·s) compared with NB (0.20 ± 0.05 m·s) (p < 0.001). Experienced benchers recorded greater RPE than NB at 1RM (EB: 9.86 ± 0.14 vs. NB: 9.35 ± 0.36) (p = 0.011). No between-group differences existed for average velocity or RPE at any other intensity. Both EB (r = 0.85, p < 0.001) and NB (r = 0.85, p < 0.001) had strong inverse significant correlations between average velocity and RPE at all intensities. Our findings suggest that the RIR-based RPE scale may be an efficacious approach for AR of bench press training load and volume in college-aged men.

The Effect of Casein Protein Prior to Sleep on Fat Metabolism in Obese Men.

We have previously shown that ingesting protein at night before sleep is either beneficial or non-detrimental to metabolism, health, and body composition in obese women. However, the overnight protein-induced lipolytic actions and mechanism for improved metabolism and body composition have not been fully established. Therefore, in a crossover design, twelve obese men (age, 27.0 ± 2.2 years) were randomly assigned to ingest (within 30 min of sleep) casein protein (CAS, 120 kcal) or a non-nutritive placebo (PLA) before going to sleep. Markers of fat metabolism (lipolysis, substrate utilization, growth hormone), insulin, glucose, resting energy expenditure (REE), and appetite (questionnaire and ghrelin) were measured. During sleep and the next morning, interstitial glycerol from the subcutaneous abdominal adipose tissue (SCAAT) was measured using microdialysis. There were no differences in SCAAT glycerol (overnight: CAS, 177.4 ± 26.7; PLA, 183.8 ± 20.2 µmol/L; morning: CAS, 171.6 ± 19.1; PLA, 161.5 ± 18.6 µmol/L), substrate utilization, REE, or any blood markers between CAS and PLA. Desire to eat was greater for CAS compared to baseline (p = 0.03), but not different from PLA (baseline: 39 ± 6, CAS: 62 ± 8, PLA: 55 ± 5 mm). CAS consumption before sleep did not affect fat or glucose metabolism, REE, or suppress appetite in hyperinsulemic obese men. CAS may be consumed before sleep without impeding overnight or morning fat metabolism in young, obese men.

Impact of Four Weeks of a Multi-Ingredient Performance Supplement on Muscular Strength, Body Composition, and Anabolic Hormones in Resistance-Trained Young Men.

Although multi-ingredient performance supplements (MIPS) have increased in popularity because of their array of ergogenic ingredients, their efficacy and safety remain in question. The objective of this study was to determine the impact of supplementation with T+ (SUP; Onnit Labs, Austin, TX, USA), an MIPS containing long jack root, beta-alanine, and branched-chain amino acids, and other proprietary blends, on strength, body composition, and hormones in young resistance-trained men. Subjects were randomized to consume either T+ (SUP; n = 14; age, 21 ± 3 years; body fat, 18.3 ± 4.7%) or an isocaloric placebo (PL; n = 13; age, 21 ± 3 years; body fat, 21.5 ± 6.2%) for 4 weeks. Both groups underwent a progressive, 4-week high-intensity resistance training protocol. Before and after the training protocol, mood state, body composition, blood hormones (also collected at midpoint), and maximal strength were measured. SUP had significantly greater increases in bench press (SUP, 102 ± 16 kg to 108 ± 16 kg vs. PL, 96 ± 22 kg to 101 ± 22 kg; p < 0.001) and total weight lifted (SUP, 379 ± 59 kg to 413 ± 60 kg vs. PL, 376 ± 70 kg to 400 ± 75 kg; p < 0.001) compared with PL. Additionally, deadlift strength relative to total body mass (calculated as weight lifted/body mass; kg:kg) (2.08 ± 0.18 to 2.23 ± 0.16; p = 0.036) and lean mass (2.55 ± 0.19 to 2.72 ± 0.16; p = 0.021) increased significantly in SUP but not PL (2.02 ± 0.30 to 2.15 ± 0.36 and 2.56 ± 0.31 to 2.70 ± 0.36, respectively). No other significant differences were detected between groups for the remaining variables. Supplementing with SUP enhanced resistance training adaptations independent of hormonal status, and thus SUP use may warrant inclusion into peri-workout nutrition regimens. This study was registered with clinicaltrials.gov (identifier: NCT01971723).

Lower potassium intake is associated with increased wave reflection in young healthy adults.

BACKGROUND: Increased potassium intake has been shown to lower blood pressure (BP) even in the presence of high sodium consumption however the role of dietary potassium on vascular function has received less attention. The aim of this study was to evaluate the relationship between habitual intake of sodium (Na) and potassium (K) and measures of arterial stiffness and wave reflection. METHODS: Thirty-six young healthy adults (21 M, 15 F; 24 ± 0.6 yrs; systolic BP 117 ± 2; diastolic BP 63 ± 1 mmHg) recorded their dietary intake for 3 days and collected their urine for 24 hours on the 3rd day. Carotid-femoral pulse wave velocity (PWV) and the synthesis of a central aortic pressure waveform (by radial artery applanation tonometry and generalized transfer function) were performed. Aortic augmentation index (AI), an index of wave reflection, was calculated from the aortic pressure waveform. RESULTS: Subjects consumed an average of 2244 kcals, 3763 mg Na, and 2876 mg of K. Average urinary K excretion was 67 ± 5.3 mmol/24 hr, Na excretion was 157 ± 11 mmol/24 hr and the average Na/K excretion ratio was 2.7 ± 0.2. An inverse relationship between AI and K excretion was found (r = -0.323; p < 0.05). A positive relationship between AI and the Na/K excretion ratio was seen (r = 0.318; p < 0.05) while no relationship was noted with Na excretion alone (r = 0.071; p > 0.05). Reflection magnitude, the ratio of reflected and forward waves, was significantly associated with the Na/K excretion ratio (r = 0.365; p <0.05) but not Na or K alone. PWV did not correlate with Na or the Na/K excretion ratio (p > 0.05) but showed an inverse relationship with K excretion (r = -0.308; p < 0.05). CONCLUSIONS: These data suggest that lower potassium intakes are associated with greater wave reflection and stiffer arteries in young healthy adults.