Bilateral or Unilateral Training for the Lower Body?

As emphasised by Zatsiorsky & Kraemer (2006) and Stone et al., (2007), and reinforced by Appleby et al., (2018), specificity and transfer are important considerations when designing resistance training programmes.

Maximising adaptations from resistance training to athletic performance is vital in programming resistance training (Appleby et al., 2018). This can be better understood by understanding the risk versus reward. There are no ‘bad’ exercises. However, understanding how effective an exercise will be, and the transfer to athletic performance, as well as understanding the individual’s needs, training age, injury history, goals, recovery time etc. will all play a role in exercise selection. If an exercise provides a greater transfer to athletic performance with a reduced risk of injury, it’s a no brainer to include in your programming.

The transfer of strength in bilateral exercises such as squats, deadlift and power cleans to improved performance has been well established (Comfort et al., 2012, Harris et al., 2008, Hoffman et al., 2004). One major advantage of such exercises is the magnitude of external load involved and the resulting development of maximal strength (Stone et al., 2003, Comfort et al., 2012, Seitz et al., 2014). This has resulted in these exercises being frequently incorporated into resistance training programmes for athletes (Appleby et al., 2018).

However, given the unilateral nature of many sporting actions such as sprinting and changing direction (Appleby et al., 2018), unilateral exercises are deemed more sport specific (Santana, 2001, McCurdy & Conner, 2003). Neuromuscular differences have been reported between bilateral and unilateral movements (McCurdy et al., 2010, Andersen et al., 2014), and unilateral exercises require more neuromuscular coordination in order to be successfully performed. This is attributed to the greater stability requirements of the unilateral exercise and the neuromuscular control required for efficient performance (McCurdy et al., 2010). Although, this is also coupled with reduced external loading when compared to bilateral exercises (Behm et al., 2002, McCurdy et al., 2010, Lawrence & Carlson, 2015). It has been suggested that the closer the mechanical specificity of a training exercise to a sporting movement, the greater the transfer of performance gain (Stone et al., 2007). Therefore, the reduced external load does not seem to be a limiting factor with regards to performance benefits. Appleby et al., (2018) suggest that the transfer of exercise to performance is dependent on contraction type, contraction velocity, and joint angle between the training stimulus and the performance; the closer the two, the greater the transfer (Stone et al., 2007).

A study in 2018 conducted by Appleby et al., investigated the development of lower body strength using either bilateral or unilateral lower body resistance training. The investigation consisted of an 8-week training programme, involving 2 lower body, volume-load matched resistance sessions per week (6 - 8 sets x 4 - 8 reps at 45 - 88% 1RM), differing only in the prescription of a bilateral or unilateral resistance exercise. The authors compared a back squat and a barbell step-up. Lower body maximal strength testing was evaluated by a 1 repetition maximum (1RM) squat and step-up.

The results of the study demonstrated that lower body strength can be developed using bilateral or unilateral exercises and that strength can be transferred between movements. The findings of the study support the use of unilateral or bilateral exercises for improved strength development. In accordance with the principle of specificity, both the bilateral and unilateral training groups demonstrated moderate improvements in their trained movement. In addition, both groups also demonstrated small improvements in the non-trained movement, indicating a level of transfer between the exercises. These findings are similar to research in the bilateral and unilateral training investigations of McCurdy et al., (2005) and Speirs et al., (2015).

Both bilateral and unilateral exercises can be used to build strength. Unsurprisingly, larger increases in strength will be seen in the exercise that is trained, for example training barbell step-ups will lead to strength gains in that exercise. However, there seems to be some transfer of strength between unilateral and bilateral exercise, as per the study of Appleby et al., (2018). This could be due to a strength increase in the legs independently, or improvements in balance, stability and neuromuscular coordination.

Therefore, it can be suggested that programming lower body unilateral exercises will lead to increases in strength not only unilaterally but bilaterally as well. This will be hugely beneficial in instances where training programmes need to be adapted for injuries or individual athlete or client needs. The lower external loading used in unilateral exercises may unload anatomical structures, which may benefit athletes or clients with acute or chronic injury who cannot tolerate large external loads.

Some benefits of lower body unilateral exercises are that both limbs must do the same amount of work which will be hugely beneficial in addressing muscular imbalances. Balance and core stability will also be challenged, with a 2012 study by Saeterbakken & Fimland finding that unilateral exercises more effectively activated core musculature than bilateral exercises. It can also be argued that unilateral lower body exercises are more sport specific, as any sport that involves running will require most actions to be performed off one leg. Whether it is sprinting, throwing, jumping or changing direction, it's rare for both feet to be on the ground during these movements.

Bilateral lower body exercises such as the back squat or deadlift can increase the efficiency of a workout. Often, it is possible to subject athletes or clients to higher loads in these exercises. In sports where athletes experience significant forces such as rugby union, this is crucial. By training both limbs at the same time, you also don’t need to worry about the effects of fatigue between training each limb and the impact this has on the central nervous system. When training heavy on a unilateral exercise, an athlete has to perform an equal number of reps on the other limb while in a fatigued state. It is highly likely therefore, that the effort levels can differentiate between limbs.

When deciding what lower body resistance exercises to include in your athletes or clients training programmes, first think about their needs and the demands of their sport and work back from there. Both bilateral and unilateral lower body exercises have a place in resistance training programmes. However, the extent of which will be governed by the above.

Train smart,

Joe

References

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