Strength training: are two limbs better than one?

No matter who you are or what sport you play, strength training matters. Even if strength training were not to positively impact your performance, it would still be critical to prevent age-related losses in muscle function. And even if you’re still young, the stronger you are now, the better your strength will remain as you age. Strength training then is not controversial, but what is controversial is how athletes should strength train.

There are entire industries dedicated to promoting different types of strength training, both within the context of performance training, as well as fitness as a whole. There are advocates for using resistance bands, barbells, kettlebells, dumbbells, or just bodyweight. There are those who argue about whether high volume, low volume, high intensity, or moderate intensity is best. Some believe in training to failure while others do not.

Unilateral vs. bilateral strength training

One of the biggest controversies of all is the debate between unilateral and bilateral strength training – ie training the right and left legs/arms independently or together. This is especially true in regard to lower body strength training. Strength training for sport has its origins in the competitive sports of powerlifting and weightlifting - sports consisting entirely of barbell movements. And as a result, much of the early strength training in sport was performed with a bias towards bilateral training, where both sides of the body are worked simultaneously.

However, over time, proponents of unilateral training began to emerge. The argument was an intuitive one; ‘If most sports happen on one leg, or at least the legs are doing different things at different time, shouldn’t the strength training reflect that?’ As unilateral training looks more specific, and feels more specific, it seemed obvious that it was more specific and should thus lead to improved sports performance. This was a compelling argument for many, and an emphasis or an exclusive focus on unilateral training became more popular.

On the other hand, proponents of bilateral training made the argument that strength training is inherently non-specific, and so trying to replicate sports movements by using unilateral training is missing the point. They argued that the point is to get strong and develop the force production capabilities of the body. They believed using bilateral training is most effective because it allows for the largest loads to be used. They also argued that by practicing the athlete’s sport, all of the unilateral adaptations will take care of themselves.

So, what the answer?  an answer even possible? There are a lot of conflicting opinions, anecdotes, and even a lot of studies examining the topic. But how can we cut through all of the noise to get some practical perspective on the topic? To provide some clarity using evidence from a range of previous studies as to which approach might be best, a group of researchers from China decided look at all of the relevant data to see what’s what by conducting a meta study (a study that pools data from a number of previous studies)⁽¹⁾.