Bilateral vs Unilateral Training in Injury Rehabilitation
Introduction
In current strength and conditioning, the question of whether unilateral strength training is more beneficial than bilateral strength training is a common one. Bilateral training involves exercises that engage both sides of the body simultaneously, whereby both sides of the body share the load and force of an exercise; these exercises are common in training programmes, as they work well to activate multiple muscles and increase full-body fitness levels (Botton et al., 2016). Unilateral exercises are also beneficial in training; these exercises train one limb individually, with the entire load and force going through one limb (Migiano et al., 2010). This exercise provides a more specific strengthening, often used to decrease muscle strength asymmetry between limbs or muscle groups (Migiano et al., 2010; Botton et al., 2016). There are advantages and disadvantages of both methods of training; Gonzalo-Skok et al. (2017) studied the differences gained following separate bilateral and unilateral training programs and found that both programs increased participant’s physical fitness, however only unilateral training reduced any muscle strength asymmetry that was present between limbs.
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Bilateral Limb Deficit
Recently, many coaches and athletes are utilising a unilateral training approach, as it has been suggested that the overall force one can exert unilaterally is greater than that of their bilateral force ability (Beurskens et al., 2015). If there is a difference in this force exertion, it is known as a bilateral limb deficit (BLD) (Kuruganti et al., 2011; Botton et al., 2016). There is no conclusive evidence explaining the cause of BLD, however one explanation is a differences in muscle activation patterns between limbs, resulting in a weaker power output (Kuruganti et al., 2011). Due to this phenomenon, increased resistance strength training may be achieved when training unilaterally, resulting in an increased maximal force production than possible through bilateral training (Costa et al., 2015). However, the evidence and scientific support behind this theory is inconsistent and scarce, therefore further research is required (Škarabot et al., 2016).
Rehabilitation
During acute injury rehabilitation, clinicians often advice the use of bilateral exercises due to high levels of pain, leading onto more unilateral weight-bearing exercises, to produce more load through specific structures, as well as aiding the correct activation of muscles (Ayotte et al., 2007). Often in early rehabilitation, when pain causes inactivity, it is difficult to find exercises to ensure muscle activation continues, and to reduce chance muscle atrophy. Scott (2016) found that inactivity for two weeks following injury can lead to a strength decrease of up to 33%, with it taking up to three times this period to regain this strength. However, a new idea called the cross-education effect suggests that unilateral strength training, for example on an uninjured limb, can enhance the strength of the same muscle group of the contralateral side, such as the injured limb (Dragert and Zehr, 2011; Scott, 2016; Escamilla-Galindo et al., 2017). The theory behind this effect relies on the stimulation of commissural interneurons at the spinal cord following unilateral strength training, with these neurons then activating contralateral motor neurones, thus potentially increasing their strength abilities (Escamilla-Galindo et al., 2017). This idea was originally used for stroke patients, however more recently it has been linked to the use in the management of acute musculoskeletal injury, where there are high levels of pain and limited movement (Scott, 216). However there is not an abundance of research into this and injury rehabilitation yet (Dragert and Zehr, 2011).
Muscle Strength Asymmetry
Unilateral strength training has been shown to decrease strength asymmetry between limbs, as well as between muscle groups of the same limb (Ayotte et al., 2007). Muscle strength asymmetry either between limbs or in the same limb has a large part to play in sporting injuries, especially in football (Yanci and Camar, 2016). Studies by Carvalho et al. (2016) and Nunes et al. (2018) found that strength imbalances in the lower limb of footballers results in a significantly high risk of hamstring injury (Ekstrand et al., 2011). When playing football, jumps and forceful movements are generally performed unilaterally, thus unilateral strength is integral for footballers (Yanci and Camar, 2016). Interestingly, Daneshjoo et al. (2013) discovered that it is the physical demands and unique movement patterns required in football that result in these muscle strength imbalances, thus believed this cannot be overlooked, urging trainers and coaches to work on reducing the muscle strength asymmetry, to reduce the risk of injury. Carvalho et al. (2016) supported this, suggesting that appropriate unilateral muscle strengthening programmes should be put in place for footballers to decrease this muscle strength imbalance, and decrease the risk of muscular injuries in football.
Combining Bilateral and Unilateral Training
Although current research is supporting the use of unilateral strength training, as an extremely useful method of BLD prevention, allowing a greater force production, as well as reducing muscle strength asymmetry to potentially reduce injury risk, especially in footballers. However, it is believed that a combined training approach which aims to utilise both bilateral and unilateral exercise is the most beneficial for athletes. Makaruk et al. (2011) suggested that clinicians should involve both methods of training to reduce muscle atrophy when injured, and to aid muscle strengthening. A study by Ramírez-Campillo et al. (2015) concluded that training with a combination of bilateral and unilateral training is the most beneficial for overall improved performance in football players. This is supported by Speirs et al. (2016) who found that both bilateral and unilateral training were equally effective at increase strength of the lower body in rugby players, therefore a combined approach would be the most advantageous.
Conclusion
Unilateral strength training has been theorized to produce a number of benefits; however many of these ideas are lacking scientific support. The BLD theory suggests that unilateral training can result in increased force production (Kuruganti et al., 2011; Costa et al., 2015; Botton et al., 2016); with the cross-education effect being useful in early rehabilitation through training the uninjured limb (Dragert and Zehr, 2011; Scott, 2016; Escamilla-Galindo et al., 2017). Another potential benefit of unilateral training is the reduction in muscle strength asymmetry, thus reducing injury risk (Ekstrand et al., 2011; Carvalho et al., 2016; Yanci and Camar, 2016; Nunes et al., 2018). Overall, combining bilateral and unilateral training is thought to be the optimal method of training, to gain all of the benefits (Makaruk et al., 2011; Ramírez-Campillo et al., 2015; Speirs et al., 2016).
References
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