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Shelley Garrett Strength and conditioning module ASPH05 Article 2: The importance of unilateral strength training Introduction Many lower body functional movements seen in most sports i.e. running, throwing, hitting, kicking, jumping and changing direction are all performed in a Unilateral manner as opposed to bilateral (McCurdy et al , 2005). In order to improve athletic performance the exercises undertaken in training should resemble those movement patterns for any particular sports (Beachle and Earle , 2008). However evidence has indicated that the two-leg squat is the exercise most commonly used by athletes to increase lower body strength (McCurdy et akl, 2010). This may be due to the fact that a single leg squat may not be able to produce as much muscular force as a two-leg squat due to the reduced base of support creating instability and therefore making the exercise more difficult to perform with resistance (Behm et al , 2002). This article looks at research on training unilaterally vs bilaterally and the effects on athletic performance. It briefly covers ways to identify bilateral differences and exercises to address this. Bilateral Vs unilateral A study carried out by McCurdy et all (2005) on the short term effects of unilateral and bilateral training found that a unilateral trained group significantly improved unilateral jump height over a bilateral trained group. A similar study by Delcore et al (1998) on female volleyball players found that unilateral plyometric training improved unilateral and bilateral vertical jump more than bilateral training. McCurdy et al (2005) study also showed that unilateral and bilateral training had the same improvement results on the second test, which was the Margaria kalamen stair climb test. According to this study using only unilateral training in a program does not reduce short term bilateral strength and power gains in untrained individuals. A further study carried out by McCurdy et al in 2010 compared EMG activity in selected hip and knee muscles when performing a two leg squat (TLS) and a modified single leg squat (MSLS). They found that the MSLS produced greater hamstring and gluteus medius activity, and the TLS produced higher rectus femoris activity. They found that the TLS produced greater quadracep:hamstring EMG ratio and indicated this may lead to muscle imbalance at the knee. They suggested that by adding MSLS (lower quadraceps:hamstring EMG ratio) to a strength training programme which had a, this may maintain the muscle strength balance at the knee. Bilateral asymmetry Strength and flexibility asymmetries between the two limbs and the strength raito between the agonist and antanogist muscles play an important role in sports with asymmetric kinetic movement patterns like soccer (Rahnama et al, 2005) Team sports athletes may develop bilateral strength differences due to favoring the dominant side in play and training (Zakas, 2006). A study carried out on English Soccer players in 2003 by Rahnama et al concluded that the knee flexors of the preferred leg might be associated differential use of the muscles during kicking and possibly lead to muscle imbalance and therefor increased risk of injury. Knapik et al (1991) found that athletes are at higher risk of injury with contralateral strength differences. For this reason it is vitally important that programs are designed to address muscle imbalances. Addressing bilateral differences Assessing bilateral difference can be done without equipment by a single leg vertical jump, although this may not be a s reliable as the preferred more common way of using an isokinetic dynamometry (Comfort & Graham-Smith, 2009). One example of a unilateral exercise that would replicate the jumping and movement patterns in many team sports would be the barbell step up. As described by Gamble (2013) this exercise plays an important role in developing strength of team sports players. It comprises of simultaneous hip and knee extension executed from a unilateral base of support. Other examples of unilateral exercises include single leg squats, Bulgarian split squats, single leg Romanian deadlifts and unilateral plyometric drills. (Comfort & Graham-Smith, 2009). Considerations Cross education Cross education has been shown to take place when training one limb only. This is process by where training only one limb can result in strength gains also in the untrained limb. Research has shown this can be up to 22%. This suggests that training one limb only can result in central neural adaptations. (Baechle and Earle, 2008). Bilateral deficit This is where; in untrained individuals the sum of the force generated by both limbs is less than that of a single limb. This can be reduced with bilateral training. (Baechle and Earle, 2008). Conclusion Based on the finding of research papers it appears that there is a favourable sway towards bilateral strength training even though most sporting movements are more unilateral in nature. There appears to be more quadriceps activity on two leg squats and more hamstring and gluteus medius activity on single leg squats indicating that both exercises should be included in a strength training programme in order to maintain muscle strength balance at the knee and hip. Studies have identified that sports such a soccer can lead to muscle imbalances due to favouring the dominant limb in play and training which would indicate a needs to identify and address any bilateral differences as studies have indicated that this factor can put athletes at a higher risk if injury. Testing for bilateral differences can be done with simple tests without using specialised equipment however this will only identify a difference in the limb and not the specific muscle/muscle group. References Baechle, T. and Earle, R. (2008) Essentials of strength training and conditioning. (3rd ed.) USA: Human Kinetics. Behm, D., Anderson, K. and Curnew, S. (2002) Muscle force and neuromuscular activation under stable and unstable conditions. J Strength cond res. Vol. 16: 416422. Comfort, P. and Graham-Smith, P. (2009) Training considerations for athletes with lower limb muscle imbalance. UKSCA . Vol. 15: 4. Delcore, G., Mathieu, W., Salazar, W. and Hernandez, J. (1998) Comparison between one leg and two leg plyometric training on vertical jump performance. Med. Sci. Sports Exerc. . Vol. 30: suppl. KNAPIK, J., Bauman, C., Jones , B., Harris , J. and Vaughan, L. (1991) Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes . AM J Sports med. Vol. 19, No. 1: 76-81. McCurdy, K., O'Kelley, E., Kutz, M., Langford, G., Ernest , J. and Torres, M. (2010) Comparison of lower extremity EMG between the 2-leg squat and modified single -leg squat in female athletes. Journal of sport rehabilitation. Vol. 19: 57-70. McCurdy , K., Langford, G., Doscher, M., Wiley, L. and Mallard, K. (2005) The effects of short term unilateral and bilateral lower body resistance training on measures of strength and power. Journal of strength and conditioning research . Vol. 19: 9-15. Rahnama, N., Lees , A. and Bambaecichi, E. (2005) A Comparison of Muscle strength and flexibility between the dominant and non dominant leg in English Soccer players. Ergonomics. Vol. 48: 11-14. Zakas, A. (2006) Bilateral isokinetic peak torque of quadriceps and hamstring muscle in professional soccer players with dominance on one or both sides. J Sports med phys Fitness. Vol. 46: 28-35.