Science-Based Weight Training

Training for strength is the most important and effective exercise that you can do, and virtually everyone, from teenagers to the elderly, can and should engage in it regularly. It’s important for the gaining and maintenance of muscle mass, one of the most underrated factors in health, which maintains insulin sensitivity, prevents heart disease and cancer, and keeps older people from losing muscle mass (sarcopenia) and descending into frailty and dependence.

But it really pays dividends to know something about the topic of weight training and how to do it. Unfortunately, the beginning (and even veteran) weight trainer can get a lot of bad advice, so taking a look at what scientific studies have found about the most effective weight training methods can set the strength trainer on the right path.

Misconceptions and wrong ideas abound in weight training, probably because so many enthusiastic amateurs are involved in it. In this article, I’ll try to clear up some of the misconceptions with a look at at science-based weight training.

In recent articles, we saw that brief workouts, at 15 minutes, done infrequently, at twice a week, can produce significant strength gains. We saw that compound lifts, not isolation lifts, are the most effective strength exercises, and are essential for the serious strength trainer. And we saw that hard weight lifting causes muscle damage, which necessitates recovery time.

Here I’ll focus on what science has to say about additional aspects of weight lifting (resistance training). These come from “Evidence-Based Resistance Training Recommendations” by Fisher et al.1 (Full paper.)

Intensity of Effort

When you lift weights, muscle fibers are “recruited”, which means that as repetitions continue and become more difficult, the body demands that more muscle fibers come into play and perform work. At the final repetition, the point of failure, all muscle fibers possible are recruited, and this is the most important step in muscle growth (hypertrophy).

Recommendation: Train to momentary muscular failure in order to recruit all possible muscle fibers. Do not train to a set number of repetitions. (For more on this, see my article on high-intensity training.)

Load and Repetition Range

If a set of repetitions is performed to failure, it makes little to no difference how much weight (load) you use. This comes with the caveat that there are limits to this. For instance, if you choose a weight with which you can do 30 reps, or 1 rep, these are unlikely to optimally recruit muscle fibers. But otherwise, studies have found little difference on muscle hypertrophy in lifting heavy weights (90% of max possible, or 90%RM), or lighter weights (30%RM), so long as the lift is done to failure. However, heavier weights (80%RM) appear to increase bone mineral density more than lighter.

Recommendation: Select a weight of 80%RM and do reps to failure, which is optimal for strength, muscular endurance, and bone density.

Repetition Duration

Repetition duration refers to cadence, that is, the amount of time it takes to perform 1 rep, i.e. slow vs fast. Repetitions should be done at a slow enough pace that muscular tension is always maintained. Fast reps or using momentum — jerking the weights around — do not maintain muscular tension.

Recommendation: Lift slowly enough to maintain muscular tension. In extreme cases, this may be 10 seconds up, 10 down, though that doesn’t appear to be necessary. I use a cadence of 4–5 seconds up, same down.

Rest Intervals

This is the time spent between sets, and the preponderance of scientific evidence shows that it has little effect on strength gains.

For pure muscle growth, don’t worry about rest intervals. Take as much or as little time as you like.

However, rest intervals may make a difference to cardiovascular conditioning. If you want to emphasize the cardiovascular aspect of training, short rest intervals are better.

Recommendation: Select your own rest interval for muscle growth. Use short rest intervals for cardiovascular conditioning.

Volume and Frequency

These refer to the number of sets and the frequency of training sessions, and this area shows probably the greatest disparity between what most people, including veteran lifters, believe, and what the science says.

There’s little evidence that performing more than 1 set of each exercise increases muscle growth, if that 1 set is done to failure.

There’s little evidence to support any recommendation as to frequency. Some studies have reported no difference with a training frequency of once vs twice a week, other studies showing no difference between twice or three times a week. My own experience tells me that you can trainso long as you feel fully rested and recovered.

Recommendation: Single set training appears to be as effective as multiple sets for muscle growth. There’s little scientific evidence for a recommendation as to frequency of training.

Endurance Training and Lifting

Some people worry that doing endurance training might hinder their lifting gains. There’s no evidence that it does, so do endurance training also if that’s what you want to do. However, additional training may hinder recovery time.

Recommendation: Endurance training doesn’t hinder muscle growth.

Range of Motion

Most trainers recommend you use a full range of motion for each rep in order to get the most growth. But there’s no evidence for this. A restricted range of motion appears to increase strength and size as much as full range.

Recommendation: Use any range of motion you like.

Machines vs Free Weights

Another controversial area. Evidence directly comparing the two is meager, but machines do increase size and strength. A muscle doesn’t know whether you’re using a machine or a barbell.

Machines may make it easier to perform a lift to failure. For instance, trying to go to failure on a set of squats is asking for trouble, namely injury. Not a problem to do so on a leg press or hack squat machine.

Just about the only barbell exercise that I’m aware of that has no machine equivalent is the deadlift.

Recommendation: Use either machines or free weights as you wish.

Training and Detraining

A mere 3 weeks of training is enough to produce muscle growth in untrained people.

Of more interest, how long does it take, when no training is done, to lose muscle strength?

Again, 3 weeks of no training appears to have little to no effect on muscle strength. Most dedicated lifters don’t ever take that much time off, but this shows that allowing adequate rest between training sessions, even of considerable length, will not hurt gains.

Recommendation: If you feel the need to take some time off, or just can’t manage to get to the gym for awhile, don’t worry about it.


Many of these recommendations are to a greater or lesser extent at odds with common training methods, the kind that you hear from a trainer or gym bro.

It’s entirely possible that scientific studies miss some important aspects of training that come from years of bodybuilding experience. Resistance training studies normally last only about 12 weeks, and most have been done using untrained people.

But, when science looks at techniques, muscle protein synthesis, frequency of training, and the like, these are the conclusions, and they form our base of knowledge as it relates to weight training.

If I had to pick a single one of the above recommendations to emphasize, it would be intensity of effort, which appears to be the single most important aspect in attaining growth in strength and size.

PS: For much more on the health benefits of strength training as well as how to begin a training program, see my book Muscle Up.

  1. Fisher, James, et al. “Evidence-based resistance training recommendations.” Med Sport 15.3 (2011): 147–162.