What resistance training actually does, how strong the evidence is for each claim, and which benefit is routinely overstated.
Josie Winfield
Head of Training · 9 January 2023 · 5 min read
Reviewed by
Glenn Coburn
Curriculum Manager at YMCAfit, tutoring and assessing since 2013
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Resistance training is any exercise in which your muscles work against a load. That load can be free weights, machines, resistance bands or your own body weight. It is also called strength training or weight training, and the terms are used interchangeably.
The UK Chief Medical Officers’ physical activity guidelines recommend that adults do muscle strengthening activity on at least two days a week, alongside their aerobic activity. Below are eight benefits, each with a note on how well supported it actually is, because they are not all on equal footing.
| Benefit | What happens | Strength of evidence |
|---|---|---|
| Muscle strength and endurance | Consistent and substantial improvements when load is progressed over time | Strong |
| Bone mineral density | Loading the skeleton helps maintain, and can improve, density at the sites being loaded | Strong |
| Mood and depressive symptoms | Meta-analysis of randomised trials shows reduced depressive symptoms | Strong |
| Body composition | Helps preserve lean mass while in a calorie deficit. Modest effect on fat loss on its own | Moderate |
| Blood pressure and cardiovascular markers | Modest reductions in resting blood pressure, best alongside aerobic exercise | Moderate |
| Sleep quality | Small to moderate improvements reported across trials | Moderate |
| Range of motion | Training through a full range improves flexibility comparably to static stretching | Moderate |
| Resting metabolic rate | Rises a little as muscle mass increases, but the practical effect is small | Weak, and commonly overstated |
Evidence strength is a summary judgement, not a formal grading.
Progressive resistance training increases both strength and muscle size. Hypertrophy is the increase in cross-sectional area of muscle fibres, and it is driven mainly by mechanical tension and a sustained rise in muscle protein synthesis. Muscle damage can occur during hard training, but damage is not what causes growth and it is not what hypertrophy means. Strength gains also come from the nervous system learning to recruit muscle more effectively, which is why beginners get stronger faster than they get bigger.
Muscular endurance, the ability to repeat contractions without fatiguing, improves alongside strength, particularly with higher repetition work.
Bone responds to load in a broadly similar way. Loading a bone stimulates adaptation at that site, which is why resistance training and weight bearing activity such as walking and running both support bone health, and why they are recommended as part of managing the risk of osteoporosis.
Resistance training burns calories during a session and raises energy expenditure for a period afterwards. On its own it is a slower route to fat loss than most people expect, because the calorie cost of a session is modest. What it does reliably is preserve muscle while you are eating less, which is why body composition tends to improve more when training and diet change together.
One claim worth correcting. Added muscle does increase resting metabolic rate, but muscle burns roughly 13 kilocalories per kilogram per day at rest, so a realistic amount of new muscle adds tens of calories a day, not hundreds. It is a real effect and a small one. Resistance training is worth doing for strength, health and body composition, not for a transformed metabolism.
The mental health evidence is stronger than most people realise. A meta-analysis of randomised trials found resistance exercise training significantly reduced depressive symptoms, and the effect did not depend on whether participants got measurably stronger. Improvements in sleep quality are reported across trials too, though the effects are smaller and the research is less consistent.
On cardiovascular health, resistance training produces modest reductions in resting blood pressure and favourable changes in blood lipids. It complements aerobic exercise rather than replacing it, and the guidance to do both stands.
Training through a full range of motion also improves flexibility. Controlled comparisons have found full range resistance training improves range of motion to a similar degree as static stretching, which is a useful counter to the idea that lifting makes you stiff.
Two sessions a week covering the major muscle groups meets the UK guidelines and is enough to see the benefits above. Start with a load you can control for the full prescribed range, add weight or repetitions gradually, and give each muscle group a day or two before training it hard again.
Technique matters more than load at the start. If you have a health condition, are pregnant, or are returning from an injury, speak to a suitably qualified health professional before starting a new programme.
Rewritten to correct the description of muscle hypertrophy, to scale back an overstated claim about metabolism, and to add citations for the health claims, which the original made without sources
Josie Winfield
Head of Training
Josie has worked in fitness for eight years, first as a personal trainer and now as a tutor and assessor at Create. She has competed in CrossFit at elite level and specialises in nutrition.
Reviewed by Glenn Coburn, Curriculum Manager at YMCAfit, tutoring and assessing since 2013.
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