Metabolism and Strength Training
Lifting weights triggers changes at the molecular level that improve human metabolism and thwart chronic disease.
Resistance training does much more than build strong muscles and bones. Research in the past few years has confirmed that lifting weights changes human metabolism in ways that improve health and well-being. That’s good news for clients with type 2 diabetes, high blood pressure, obesity and high cholesterol levels.
Resistance exercise also improves resting metabolic rate and cardiorespiratory fitness. Indeed, some authors call resistance training an exercise therapy program (Strasser & Schobersberger 2011). That’s a powerful swing of the pendulum from days when pushing barbells and mastering squats were seen primarily as ways to boost strength, muscular endurance and bone density.
This article synthesizes the major metabolic effects of resistance training, as confirmed in recent research. We also outline mechanisms leading to metabolic gains and discuss how these positive changes relate to your training clients and your fitness practice.
Diabetes and Strength Training
Diabetes mellitus affects people who do not produce insulin (type 1) or who do not respond well to insulin (type 2). The National Diabetes Statistic Report, 2017 (CDC 2017) provides the following statistics:
- About 30.3 million Americans have diabetes (9.4% of the population); 90%–95% of them have type 2. Approximately 84.1 million U.S. adults (33.9% of the population) have prediabetes, meaning they have biomarkers indicating a high risk of developing type 2 diabetes.
- Type 2 diabetes becomes more prevalent as people age: 25.2% of people 65 or older have it.
Resistance Training Studies in Diabetes Populations
Resistance training versus aerobic exercise. A 10-week study (Bweir et al. 2009) compared the effects of resistance training versus aerobic exercise on two crucial biomarkers (blood glucose and A1c) in 20 inactive men and women (average age 53) with type 2 diabetes.
The aerobic group progressed from 20 minutes of exercise at 60% of their maximum heart rate to 30 minutes at 75% of HRmax. The weightlifting group performed 3 sets of 8–12 repetitions, completing a series of exercises: knee and hip flexion/extension, shoulder flexion/extension, shoulder adduction/abduction, elbow flexion/extension, and chest press. At the end of the experiment, the resistance training group showed a more favorable decrease (-18%) in A1c than the aerobic group (-8%).
Combination training. Other researchers spent a year comparing the effects of resistance training alone, aerobic training alone and combined (resistance plus aerobic) training in 80 obese adults (37 men; 43 women) who had type 2 diabetes (Yavari et al. 2012).
Participants were divided evenly into four groups. The aerobic group trained on treadmills, ellipticals or stationary bicycles—progressing from 20 to 60 minutes at 60%–75% of HRmax—on 3 nonconsecutive days a week. The resistance group trained on weight machines 2 days per week in the first month and increased to 3 nonconsecutive days per week for the rest of the study. They initially trained 1–2 sets (first month) at 60% of one-repetition max (1-RM) and progressed to 3 sets of 8–10 repetitions at 75% of 1-RM on 10 different upper- and lower-body exercises. The combined group did the aerobic program plus the resistance program 3 days a week.
After 52 weeks, 60 study participants (15 per group) were included in a statistical analysis. A1c values favorably decreased by 1.33%, 0.55% and 1.74% in the aerobic, resistance and combined groups, respectively. The authors note that previous research suggests an A1c reduction of 0.66% is an excellent marker for improved glycemic control. The control group had an unfavorable 0.2% rise in A1c. Yavari et al. conclude that combining resistance and aerobic exercise clearly shows an additive effect for preventing or managing type 2 diabetes.
How Lifting Weights Affects Type 2 Diabetes
Studies suggest that resistance training improves glucose clearance and insulin sensitivity by increasing the concentration, activity and/or sensitivity of GLUT4, insulin receptors, protein kinase B beta and glycogen synthase (Holten et al. 2004). GLUT4, insulin receptors and protein kinase B beta are proteins that help to transport glucose into muscle cells for energy. Glycogen synthase assists in converting glucose molecules into stored glycogen in the muscle (to be used eventually for energy needs)
Moreover, an increase in lean mass from weight training may reduce visceral fat—stored around internal organs like the liver, pancreas and intestines (Strasser & Schobersberger 2011). By contrast, Strasser and Schobersberger note that losing muscle mass increases the risk of developing obesity-associated insulin resistance and type 2 diabetes. Importantly, resistance training decreases A1c levels in diabetic adults at any age.
The American Diabetes Association position statement (Colberg et al. 2016) recommends using 8–10 exercises (a total-body program). Start with 1–3 sets of 10–15 repetitions until near failure. Progress to a moderate intensity where no more than 15 reps can be performed with each set. For a vigorous weightlifting program, perform 6–8 reps to failure for each exercise. Do the training a minimum of 2, and preferably 3, days per week. To progress the program, Colberg and colleagues recommend adding more load (e.g., from 10–15 reps, progress to 6–8 reps to failure), then doing more sets (upping the number to 3) and then increasing frequency (from 2 to 3 days weekly).
See also: Weight Training and Diabetes
Blood Pressure and Strength Training
- Blood pressure generates two readings: systolic pressure during heart contraction (i.e., ejection of blood) and diastolic pressure dur┬¡ing ventricular filling.
- Normal readings are below 120 for systolic blood pressure and below 80 for diastolic blood pressure.
- High blood pressure, or hypertension, is indicated by a systolic reading of 140-plus and a diastolic reading of 90-plus. Prehypertension means the reading falls between normal range and high range (AHA 2019).
- Eighty million adults 20 and older have hypertension, which is a major risk factor for heart disease and stroke. An estimated 41.4% of adults are expected to have high blood pressure in 2030 (Mozaffarian et al. 2015).
Resistance Training Research in Hypertensive Populations
Optimum dose for blood pressure improvement. Scientists have evaluated the dose-response relationship between resistance exercise and changes in blood pressure (Westcott et al. 2009). For 10 weeks, 1,619 untrained and sedentary adults (77% women, 23% men; aged 21–80) engaged in one, two or three exercise sessions per week. Each session consisted of 20 minutes of aerobic training (70%–80% of age-predicted HRmax; rating of perceived exertion under 15) and 20 minutes of weight training (1 set; 8–12 repetitions to volitional fatigue; 10 exercises, working the whole body).
On average, systolic blood pressure fell by 3.83 and diastolic pressure fell by 1.73. The researchers concluded that two or three training sessions a week appeared to do the most good for managing or lowering blood pressure (if elevated).
Peripheral heart action. In 2015, research using peripheral heart action training provided evidence that weight training can reduce blood pressure directly (Piras et al. 2015). With PHA training, participants sequentially alternate upper- and lower-body exercises in a circuit. The theory is that this type of training enhances blood flow through the body.
Subjects performed four rounds of circuit resistance training (15 reps at 55%–60% of 1-RM) in this order: chest press, leg extension, latissimus dorsi pulldown, hamstring curl, shoulder press and heel raises (note the alternating upper- and lower-body sequence). There was no rest between sets and only 1 minute of rest between circuits.
After 30 training sessions (3 per week, on nonconsecutive days, over 3 months), PHA participants had significantly reduced their systolic (-2.59) and mean arterial (-1.69) blood pressure. Mean arterial blood pressure is the average blood pressure in a person’s arteries during one heartbeat. These results corroborate a research review by Cornelissen & Smart (2013), which analyzed 93 studies and concluded that resistance training reduces systolic pressure (-1.8, on average) and diastolic pressure (-3.2, on average).
How Weight Training Helps With Blood Pressure
Though most research on training and blood pressure focuses on the influence of cardio exercises, some interesting findings on resistance training have emerged. For instance, one experiment examined the effects of 1 year of weight training on vascular structure and function in overweight, but otherwise healthy, women (Olson et al. 2006). The primary finding was that weight training alone improved brachial artery endothelial function in this group. The endothelium is a membrane on the inside of blood vessels in the body and heart. Endothelial cells release substances that control blood vessel contraction, relaxation, clotting and immune function. They are deeply involved in blood pressure regulation.
In another study with 18- to 35-year-old adults diagnosed with prehypertension (Beck et al. 2013), an 8-week resistance training program (3 times per week) reduced peripheral blood pressure (arms, hands, legs and feet), improved endothelial function and enhanced other blood vessel substances involved in the regulation of vascular tone (the degree of constriction in blood vessels when fully open).
To protect prehypertensive and hypertensive clients and to improve endothelial function, make sure resistance training is not performed to concentric failure. In a research review (de Sousa et al. 2017), programs that successfully reduced blood pressure (when elevated) had participants doing 7–10 exercises (working the major muscles of the body) 3 days per week at 40%–80% of 1-RM. Participants progressed to 2–3 sets of 8–15 repetitions, with 60ÔÇô180 seconds of rest between sets.
RMR, EPOC and Strength Training
- Resting metabolic rate is a measure of the calories we burn at rest. RMR accounts for 50%–75% of daily caloric expenditure (Aristizabal et al. 2015). Maintain┬¡ing the body’s vital functions, such as heart rate, breathing and brain function, demands quite a lot of energy.
- Excess postexercise oxygen consumption refers to the increased rate of oxygen uptake (i.e., energy expenditure) after dynamic exercise. Specifically, EPOC is the energy the body consumes to restore its pre-exercise condition.
Resistance Training Research With RMR and EPOC
Weightlifting, RMR and supplements. One project (Aristizabal et al. 2015) recruited 61 recreationally active adults (aged 18–35) who had done no resistance training for a minimum of 1 year prior to the study. The 9-month (96-workout) experiment periodized the training into three 12-week mesocycles. These cycles included multiset (3- to 5-set) training with light-intensity sessions (12–15 reps, 60–90 seconds of rest between sets), medium-intensity sessions (8–10 reps, 1–2 minutes of rest between sets), high-intensity sessions (3–6 reps, 2–3 minutes of rest between sets) and power sessions (whole-body exercises at 30%–45% of 1-RM, 3 minutes of rest between sets). Exercises consisted of bench press, squat, hang clean, biceps curl, heel raise, abdominal exercises, latissimus dorsi pulldown, lunge, upright row, push press and weight-plate lift.
Participants were divided into 3 groups. During the 9 months, all of them did the same training sessions, but each group received a different type of supplementation (whey protein, soy protein or carbohydrate). RMR increased in participants by approximately 5%. There were no group differences in RMR increases due to the supplementation.
EPOC and exercise intensity. One unique study compared EPOC values after three workouts with similar energy expenditure (Greer et al. 2015):
- resistance training (60% of 1-RM to fatigue) with seated pectoral fly, squat, latissimus pulldown, cable triceps pushdown and heel raise in a circuit (1-minute rest between sets), repeated over 45 minutes
- moderate-intensity, steady-state aerobic training at approximately 39% of aerobic capacity, stopping when participants had burned the same number of calories as they did in the RT workout
- high-intensity interval training (HIIT), 30 seconds at 90% of aerobic capacity, followed by 120–180 seconds of relief at a light intensity until caloric burn matched the RT workout
The HIIT and resistance trials showed similar EPOC values at 12 and 21 hours after the workouts, significantly higher than the results for the steady-state aerobic trial. EPOC for the resistance/HIIT groups was 15% above baseline at 12 hours and 12% above baseline at 21 hours. In practical terms, the study calculated that weightlifting/HIIT burned an impressive 300 more calories in 24 hours than the steady-state aerobic training.
How Weight Training Influences RMR and EPOC
Muscle mass and thyroid hormones have a profound effect on RMR. Apart from building lean body mass, resistance training may trigger metabolic changes in muscle that influence thyroid hormones, though more research is needed in this area (Aristizabal et al. 2015).
Research shows that resistance training can disrupt muscle differently than aerobic training does. Resistance training leads to muscle protein synthesis and repair, which are energy-demanding metabolic processes. Higher exercise intensities produce more EPOC because they cause more muscle disturbance (Greer et al. 2015).
To boost RMR, it’s a good idea to use periodized programs in which participants cycle progressively through various aspects of training and there are systematic changes in intensity and volume (Aristizabal et al. 2015). For maximum EPOC, use compound exercises that recruit as much muscle mass as possible at higher intensities relative to a person’s fitness level (Greer et al. 2015).
See also: Women and Weight Training
Obesity and Strength Training
- A body mass index over 30 generally indicates obesity.
- About 39.8% of Americans have obesity: 42.8% of adults aged 40–59; 20.6% of adolescents aged 12–19; and 18.4% of youth aged 6–11 (Hales et al. 2017).
- Resistance exercise is a potent way to address obesity because this type of training increases lean body mass while shrinking fat mass (Strasser & Schobersberger 2011).
Research on Resistance Training in Obese Populations
Muscle mass increases. A review of research studies noted that resistance training programs typically boost muscle mass by a minimum of 2.2–4.4 pounds. Many studies show that weight training programs also reduce visceral fat, which is associated with the development of abnormal cholesterol levels, hypertension, insulin resistance, type 2 diabetes and cardiovascular disease (Strasser & Schobersberger 2011).
How Resistance Training Promotes Fat Loss
Resistance exercise causes a convergence of metabolic stress, mechanical tension and exercise damage in muscle cells, signaling the body to increase muscle protein synthesis. Repeated weight training over the course of weeks and months leads to acute increases in muscle protein synthesis, boosting muscle mass. Long-term muscle mass growth gradually increases RMR, causing greater caloric expenditure at rest and enabling weight loss.
A broad variety of resistance training techniques can increase muscle mass and reduce the risks of obesity. Recent research on weight training found that volume—sets x reps x load—is a critical factor in improving muscle mass (Schoenfeld, Ogborn & Krieger 2017).
The study found a clear dose-response relationship between the number of sets and hypertrophy, the scientific term for muscle growth. In counting weekly sets per muscle group, the researchers found that significant hypertrophy occurred with the following: <5 sets (+5.4%); 5ÔÇô9 sets (+6.5%); and >10 sets (+9.6%). This hypertrophy spectrum provides personal trainers with training guidelines that can be adjusted to suit clients’ preferences and fitness levels.
High Cholesterol and Strength Training
- Approximately 95 million U.S. adults aged 20 or older have total cholesterol higher than the recommended biomarker of 200 milligrams per deciliter, and 29 million adults have total cholesterol above 240. An estimated 7% of U.S. youth aged 6–19 also have high total cholesterol levels (CDC 2019).
- High blood cholesterol raises the risk for stroke and heart disease. The Centers for Disease Control and Prevention says healthy adults should have their cholesterol checked every 4ÔÇô6 years. Those with heart disease, diabetes or a family history of high cholesterol need to get their cholesterol checked more often.
Research on Resistance Training and Cholesterol
Fahlman et al. (2002) compared the effects of resistance training versus aerobic exercise on blood lipid profiles, the scientific term for cholesterol levels, in 45 healthy, active women (aged 70–87) whose cholesterol markers fell in the normal range. Aerobic exercise consisted of walking 3 days per week at 70% of heart rate reserve. The women walked 20 minutes on the first day and added 5 minutes per day until they reached 50 minutes after week 3.
Weight training consisted of total-body exercises performed 3 days per week, with 3 sets of 8 repetitions to momentary muscular fatigue (adjusted weekly during the 10 weeks of training). Rest between sets was 2 minutes. The regimen used 3 sets of leg extension, leg curl, plantar flexion and dorsiflexion; 2 sets of hip flexion and hip extension; and 1 set of hip adduction and hip abduction.
In 10 weeks, resistance group trainees decreased their total cholesterol markers by 10, their “bad” cholesterol (LDL) by 18.3 and their blood fats by 29, while their “good” cholesterol (HDL) rose by 10.3 units (milligrams per deciliter). The aerobic group also saw improvements in cholesterol markers, but these gains were not nearly as notable as those seen in the weight training group. Unfortunately, there’s not much research on the independent effect of weight training on cholesterol in people with abnormal cholesterol levels. Much more research is needed in this area, on both men and women.
Researchers published an excellent review summarizing how cholesterol levels respond to aerobic training, resistance exercise and combined (aerobic plus resistance) regimens (Mann, Beedie, & Jimenez 2014). Based on analysis of 13 published investigation and two review articles, the researchers concluded that an increase in volume—reps x sets x load—improves cholesterol profiles more than an increase in intensity. The scientists also suggested that blending aerobic training and weightlifting creates a synergy that drives optimal improvements in cholesterol profiles in men and women.
Can Resistance Training Improve Cardiorespiratory Fitness?
Some researchers want to know if resistance training provides an alternative path to improving cardiovascular fitness. Further knowledge is welcome because heart and lung health is a powerful predictor of all-cause mortality, regardless of pre-existing health conditions.
The most common measure of cardiorespiratory health is VO2max, the maximal rate of oxygen consumption, distribution and use for energy during exercise. A recent systematic review and meta-analysis explored circuit training programs that improve VO2max (Munoz-Martinez et al. 2017). The researchers found that circuit-based resistance training can increase VO2max by an average of 9.7%—a remarkable result. Their review recommended that programs include
- 14–30 sessions for 6–12 weeks for at least 20–30 minutes
- intensities between ~40%–80% of 1-RM
- 6–12 exercises per session, with 12–15 repetitions or 20–40 seconds of work per station
- at least two circuits overall
The options are close to unlimited for designing circuit resistance training programs to improve cardiorespiratory health. That empowers personal trainers to be creative while staying within the guidelines of established evidence.
The Science Is Clear: Resistance Works
The playbook is wide open for personal trainers who want to use weightlifting to improve clients’ metabolism. You’re limited only by your creativity and imagination. We encourage you to use a variety of resistance methods (free weights, suspension exercise, battle ropes, kettlebells, etc.) to build dynamic, fun and engaging programs that are a great match for your clients’ goals and needs.
Increasing muscle size and strength has numerous positive implications, including lowering blood pressure and cholesterol levels and improving insulin sensitivity, lipid profiles, cardiovascular function and body composition. The message is clear: Lift weights, build muscle and improve your quality of life. With every rep, we all get stronger!
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