You need to train pretty hard in order to gain strength and muscle. That's obvious. But how hard exactly? A relatively new belief in the world of strength training is that only the last few reps of a tough set truly stimulate muscle growth. This implies that you should train close to your limit if you're looking for results. The obvious way to go about doing that is to actually reach your limit each set, blasting out reps until you can no longer lift the weight ('training to failure'). Unfortunately, training to failure carries a few major downsides, so deciding on your optimal training effort is a bit more nuanced. In this article I will explain why, and provide you with some strategies for your own training.

Muscle mechanics 101

The muscles in your body all contain tons of muscle fibers, ranging from smaller to larger, and are recruited in that order. Important to note is that the largest of those muscle fibers carry the most growth potential. In training, you therefore ideally stimulate those largest muscle fibers as much as possible, which can be done by either lifting heavy weights (5RM, +-85% of your 1RM, and heavier) or by lifting lighter weights until fatigue.

During the heavy stuff the large muscle fibers will pretty much ‘turn on’ right away, making every repetition stimulating of growth. When lifting something lighter - say, a set of 20 reps - the smallest non-growing muscle fibers will first need to be fatigued before their larger brothers step in to assist (and may start growing). This means that you need to train pretty close to your limit in order to hit those largest muscle fibers, especially when lifting lighter weights. By now you probably understand why training to failure is tempting, so let's get to the downsides.

It’s better to be building than to be repairing

When training hard you damage your muscles, which expresses itself through muscle pain and reduced strength in the following days. This may leave you unable to quickly retrain a muscle, which slows your progress. It so happens that when you train to failure, the amount of muscle damage disproportionally increases in comparison to when you train just shy of failure, but without bringing along additional growth. This means that squeezing out that last ugly rep does little more than prolong your recovery time.

A second problem with training to failure is that it zaps your energy levels. It causes a lot of fatigue, which means that you’ll not be able to train as hard on following sets (or exercises) within that training session. Fewer ‘growth-stimulating reps’ are the result. If you’re not sure about this: max out a set of pull ups to failure, and notice your massive drop in performance on the subsequent set. If you try again a week later and keep one or two reps in the tank, you’ll find that you’ll be able to perform significantly more reps on the following sets. As a result, your average training intensity (defined as % of 1RM) will be much higher. Gains!

Last but not least, training to failure provokes poor technical habits. When fatigue causes you to no longer lift with the intended technique, your body will always find a more economic way move from point A to B. Think of that bending low back during deadlifts, or your ass coming off the bench while bench pressing. Although it's OK for this to occasionally happen on your quest to pushing your limits, it often entails an increased injury risk because you’re basically losing control of the movement. So tread carefully. It also engrains sloppy movement patterns, which will definitely hamper long term progress.

Growth-stimulating strategies

Ideally you get close to failure during your sets so you’ll perform a maximal amount of reps that stimulate a large amount of muscle fibers. But it’s better not to actually reach failure so you won’t unnecessarily prolong recovery time. In that respect, the trick is to get to know yourself so well that you’ll always kind of give '95%'. Maybe skip that last rep in a set of 20 if you're not sure whether you’ll be able to complete it. Or pick your 5RM weights carefully so that it feels like another 2.5 kilos on the bar would have meant stopping after rep four. When making this a habit, you'll be performing a lot of technically sound reps that stimulate growth and strength, but without tumbling down the abyss of excessive recovery times.

This will require some experimentation and discipline, but you’ll soon get the hang of it. If you’re the type that gets tempted to go all-out anyway, just keep in mind that you’re not doing yourself a favor: training to failure just keeps you on the sideline for longer.

Good luck!