UNILATERAL TRAINING

Many sports or activities of daily living involve single limbs (McCurdy and Conner 2003). However, traditional resistance exercises are often bilateral (both arms or both legs), using machines, a barbell, or a pair of dumbells. According to the specificity principle, training should simulate as closely as possible the actions of the sport or activity (Sale 1988). The greater the difference between the training movements and the sports actions, the less potential transfer can be expected (Behm 2003)
Thus to adhere to the specifity principle, unilateral, or single-limb, training should constitute a significant portion of a person’s training program.

A further advantage of unilateral training is the disruption in balance (disruptive torque) placed on the body, resulting in higher activity of the core muscles to offset the imbalance. For example, holding and moving a single dumbbell on one side of the body will cause the trunk and body to shift toward that side, resulting in increased muscle contractions of the opposite side to balance the shift. Behm, Leonard et al. (2005) reported greater back muscle activation during the unilateral shoulder press and greater lower abdominal stabilizer activity during the unilateral chest press. Instead of an unstable base, unilateral or single-limb resisted actions can provide a disruptive torque to the body, thus providing another type of unstable condition.

The greater activity of the core muscles with instability in the previous studies was not compared to the greater weights that can typically be lifted during ground-based free weight training. Squats and deadlifts using 80% of 1RM produced greater activity of the back muscles than unstable callisthenic exercises such as the side bridge and superman (Hamlyn, Behm, and Young 2007).

picture extracted from: https://www.google.es/search?q=UNILATERAL+TRAINING&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjogIHDpN_aAhVCwxQKHWSOAg8Q_AUoAXoECAAQAw&biw=1920&bih=949#imgrc=RJhQEmK2WoItvM:

In a similar study, greater back activation was reported with stable deadlift and squat exercises versus unstable callisthenic exercises (Nuzzo et al 2008). Willardson, Fontana, and Bressel (2009) reported significantly higher muscle activity for abdominal muscles during the overhead press when lifting with 75% of 1RM on stable ground versus lifting with 50% of 1RM on a BOSU ball. Conversely, there were no significant differences in muscle activity for the external obliques and back muscles for the squat, deadlift, overhead press, and biceps curl when lifting with 75% of 1RM on stable ground or with 50% of 1RM or a BOSU ball.

Overall, Willardson and colleagues not demonstrate any advantage in utilizing a BOSU ball for training the core muscles. The same research group conducted a similar experiment but added a condition where instructions were provided to the subjects to consciously activate their trunk muscles while performing a free squat with 50% of 1RM. The instruction condition was most effective for activating the abdominal muscles as compared to unstable and heavier (75% of 1RM) squats (Bressel et al 2009).

Whereas competitive athletes may be able to achieve greater core muscle activity with heavy free-weight exercises, people more interested in health or rehabilitation may choose to achieve greater core muscles activation with lower loads or weights while supported on unstable surfaces. Notwithstanding, highly trained athletes may not receive a similar balance training adaptation with moderately unstable devices. Wahl and Behm (2008) found that the use of moderately unstable devices (i.e., rubber discs, BOSU balls) did not provide as great stability challenge as the stability ball or wobble board in highly resistance-trained athletes. Because these athletes may have possessed enhanced stability from the performance of free-weight exercises, a greater degree of instability or resistance may be necessary for further adaptations. Hence the training needs and adaptations of experienced and inexperienced people suggest than their training programs should differ.

In this link you can watch an example of this: https://www.youtube.com/watch?v=ud9aTW3hvtk and in this link you can see a summary: https://drive.google.com/open?id=1S7RacvsjSaHfzx9WEiCdggxF4iNIMZ4V

BIBLIOGRAPHY

Willardson, J. M., & National Strength & Conditioning Association (U.S.). (2014). Developing the core.

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