Download Shelley Garrett Strength and conditioning module ASPH05 Article 2

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
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Rahnama, N., Lees , A. and Bambaecichi, E. (2005) A Comparison of Muscle strength
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