The beneficial effects of exercise on physical and mental health are well acknowledged (Surakka et al., 2002). Having a healthy lifestyle and being active is something that everyone tries to achieve in this modern society, with this way of life ever increasing more people are commonly becoming injured (Hootman et al., 2001).

Healthy lifestyle

Muscular strength is an important component of success in athletic performance (Bompa and Haff, 2009), it requires different motor demands depending on the required movement pattern whether this is bilateral or unilateral movements (Cowling et al., 2003). Reliance on these movement demands may cause muscle imbalances within the body this can have an effect on movement dependence on one or more muscles (Luk et al., 2014).

What is muscle imbalance?

Muscle imbalance is when one side of the opposing muscles are stronger than the other, when this happens a muscle imbalance occurs. For instance, if you regularly use the muscles on one side more than the other, they get stronger, shorter and tighter in comparison to the other side where the muscles get weaker, longer and looser.

Human movement and function requires a balance in muscle length and strength between opposing muscles and surrounding joints. Normal amounts of opposing forces between muscles are necessary to keep bones centred during joint motion. When muscles are tight and weak an imbalance occurs due to different directions of tension.

Unbalanced

When muscles are tight the joint moves in the direction of tightness but is then limited when moving in the opposite direction. The joint tends to move in the direction that has the least resistance as the body typically chooses to take the easiest route/movement. Muscle imbalance is generally linked to weakness and tightness; the majority of imbalances are due to muscle weakness rather than tightness but throughout the body we have natural imbalances.

hamstrings

For example, the quadriceps are made up of 4 bulky muscles were as the hamstrings are made up of 3 thinner and smaller muscles.

 

 

Quads

 

Common muscle imbalances are found around joints as the muscles help to stabilize and protect the joints. Muscles include the shoulder, thigh, core and lower back, chest and upper back (Franettovich et al., 2011). Few studies have looked into specific patterns of muscle imbalance and postural abnormalities that are associated with muscle imbalance syndromes.

Another common muscle imbalance is between the rotator cuff muscles these are a group of muscles that are found in the shoulder connecting the humerus (upper arm) to the scapula (shoulder blade). These muscles help provide stability to the shoulder and allow the shoulder to rotate. The rotator cuff muscles are listed below:

  • Teres Minor – laterally rotates the arm and stabilizes the humerus
  • Infraspinatus – laterally rotates the arm and stabilizes the humerus
  • Supraspinatus – abduction of the arm and stabilizes humerus
  • Subscapularis – internally rotates humerus and stabilizes shoulder

(look at useful literature for actions of the shoulder)

Upper cross syndrome

What is it?

Upper crossed syndrome (UCS) is when you have tight pectoral muscles (chest muscles) and tight upper trapezius muscles, while having weak cervical flexors and weak rhomboids and lower trapezius. The pattern of imbalance causes a joint dysfunction which is of a kyphotic curve. The UCS is often linked to people who work in offices at a desk as posture isn’t always maintained and the head often protrudes changing centre of gravity other specific postural changes can be seen with UCS including increased cervical, lordosis and thoracic kyphosis, elevated and protracted shoulders and winging of the scapular. These changes affect the glenohumeral joint (shoulder joint) stability and often causes impingement within the glenoid fossa (socket part of the shoulder joint) (Morris et al., 2015).

UCS

What can be done about it?

The main aim of treatment is to try and balance the imbalance by stretching and strengthening opposing muscles. However as the muscles are weak it is important to stretch and stimulate the muscles to increase sensory and circulatory flow. From a clinicians view it is important to focus on the following key activities:

Lower Cross Syndrome

What is it?

Lower cross syndrome (LCS) can also be called pelvic cross syndrome. LCS is similar to UCS in the context that it is to do with weak and tight muscles. LCS was first discovered by Czech physician Vladimir Janda, he noticed that the many of his patients were very tight at the front of the hips (hip flexor muscles), the posterior muscles (hip extensors) were found to be elongated and weak (Bullock-Saxton et al., 1993). LCS often changes the tilt on the hips, the pelvis rolls forward due to the tight hip flexor muscles. The protruding weakens the abdominals as well as the gluteals and hamstring complex. It’s not just the upper part of the leg that is affected, the calf muscles become tight as well as changing the bio-mechanics of the knee, the shin muscles are also weak affecting the foot allowing it to roll inwards increasing the likelihood of an ankle ligament injury (Janda et al., 1994). Look at the diagram below to help illustrate what is being explained, shaded blue = weak muscles, shaded red = tight muscles:

LCS

What can be done about it?

Isokinetic dynamometer and how it is used to assess muscle imbalance

An isokinetic dynamometer (ISK) has become increasingly popular within rehabilitation within the past 10-15 years. The ISK allows assessment of joint movements in both static and dynamic motions and can be used as a specific exercise intervention or for rehabilitation from sports injuries. For this reason, the ISK is a useful and unique device that allows the assessment of dynamic muscle and joint function under specific velocity conditions.

Isokinetic Dynamometer

ISK measures muscle strength by recording the resistive moment required to counter balance the joint moment applied by the participant and maintain a constant joint angular velocity. Testing conditions and typical errors range from 10%-13% during isokinetic knee extensions and from 1-17% (mean 7.3%) in isometric conditions (Arampatzis et al., 2006). Isokinetic dynamometry has also been used in clinical applications to assess the effects of surgical and rehabilitative interventions on neuromuscular performance. The ISK can also be used to measure muscle imbalance by measuring the peak torque values of both the agonist and antagonist and dividing the torque for one by the other and multiplying it by 100 to get a percentage deficit. For example, if peak torque of the hamstring is 210 and the peak torque of the quadriceps is 289. H:Q, 210 ÷ 289 x 100 = 0.73%. The strength ratio between the hamstrings and quadriceps is between 50-80% with 100% being equal strength (Coombs and Garbutt, 2002).

ISK graph

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References

Arampatzis, A., De Monte, G., Karamanidis, K., Morey-Klapsing, G., Stafilids, S. and Bruggemann, G.P. (2006) Influence of the muscle-tendon unit’s mechanical and morphological properties on running economy. The Journal of Experimental Biology. Vol. 209, No. 17: 3345-3357.

Bompa, T.O. and Haff, G.G. (2009) Periodization: Theory and Methodology of Training. (5th ed.) USA: Human Kinetics.

Bullock-Saxton, J.E., Janda, V. and Bullock, M.I. (1993) reflex activation of gluteal muscles in walking. An approach to restoration of muscle function for patients with low-back pain. Spine. Vol. 18, No. 6: 704-708.

Coombs, R. and Garbutt, G. (2002) Developments in the use of the hamstrings/quadriceps ratio for the assessment of muscle balance. Journal of Sports Science & Medicine. Vol. 1, No. 3: 56-62.

Cowling, E.J., Steele, J.R. and McNair, P.J. (2003) Effect of verbal instructions on muscle activity and risk of injury to the anterior cruciate ligament during landing. British Journal of Sports Medicine. Vol. 37, No. 2: 126-130.

Franettovich, M., Hides, J., Mendis, M.D. and Littleworth, H. (2011) Muscle imbalance among elite athletes. British Journal of Sports Medicine. Vol. 45, No. 4: 348-349.

Hootman, J.M., Macera, C.A., Ainsworth, B.E., Martin, M., Addy, C.L. and Blair, S.N. (2001) Association among physical activity level, cardiorespiratory fitness, and risk of musculoskeletal injury. American Journal of Epidemiology. Vol. 154, No. 3: 251-258.

Janda, V., Bullock-Saxton, J.E. and Bullock, M.I. (1994) The influence of ankle sprain injury on muscle activation during hip extension. International Journal of Sports Medicine. Vol. 15, No. 6: 330-334.

Luk, H.Y., Winter, C., O’Neill, E. and Thompson, B.A. (2014) Comparison of muscle strength imbalance in powerlifters and jumpers. Journal of Strength and Conditioning Research. Vol. 28, No. 1: 23-27.

Morris, C.E., Bonnefin, D. and Darville, C. (2015) The Torsional Upper Crossed Syndrome: A multi-planar update to Janda’s model, with a case series introduction of the mid-pectoral fascial lesion as an associated etiological factor. Journal of Bodywork and Movement Therapies. Vol. 19, No. 4: 681-689.

Surakka, J., Aunola, S., Nordblad, T., Karppi, S.L. and Alanen, E. (2002) Feasibility of power-type strength training for middle aged men and women: Self-perception, musculoskeletal symptoms, and injury rates. British Journal of Sports Medicine. Vol. 37, No. 2: 131-136.