Joseph Dea SPT, Meynard Enriquez DPT, Tiffany Ikeda-Simao DPT, and Kaylen Wakumoto DPT
Hawaii Sports and Balance Center – Lihue, Hawaii
Champion track sprinter Usain Bolt has what was known colloquially as a “hitch in his get-along.” Despite his impressive professional career, Bolt has scoliosis, and a right leg that is approximately one half-inch shorter than his left leg, resulting in an asymmetrical stride. Asymmetry occurs in healthy athletes as well as those who are rehabilitating from injury. Assessing the importance of asymmetry in injured athletes is, therefore, not straightforward. Although “performance” during running sports seems to be unaffected by interlateral leg asymmetries likely due to the body’s ability to compensate at the hip, knee, and ankle, the research shows high prevalence of interlateral leg asymmetries with specific leg injuries. (1, 2)
Furthermore, the research suggests that as a runner you may likely be able to continue running despite leg asymmetries, however with long distance running, the negative effects of compensating for a weaker or less stable leg may be more apparent. (2) More asymmetry between legs are found in knee overuse injuries, such as those common with long distance running. (3)
Running gait asymmetry can a result of several factors including pain, leg length discrepancy, side-to-side muscle imbalance, and compensatory mechanisms. These measures are risk factors for a first-time injury or consequences of a previous injury. (4)
Injuries That Could Result from Leg Asymmetries
Hamstring Strain: In a study of sub-elite runners, it was discovered that uninjured sprinters had perfectly symmetrical ground contact times. However, injured sprinters exhibited asymmetrical times. Injured runners demonstrated significant differences in hip extension during toe off, likely resulting in their hamstring strain. (4)
ACL injuries: Changes in single limb balance were found in healthy individuals when compared to those with ACL injuries and after ACL reconstruction. Changes in single limb balance were seen between the affected and non affected leg in individuals who underwent ACL reconstruction. (5)
Tibial Stress Fractures: Although there are many factors that can contribute to stress fractures, one study found that leg asymmetries can affect which limb is injured. (1) Therefore, maintaining leg symmetry can help decrease the likelihood of injury. A recent study also found that asymmetries in foot-support dynamics differed between injured and uninjured subjects, which contributed to a higher incidence of tibial stress fractures. (6)
Foot problems: There is evidence that supports that having a lower leg length difference (LLD), where one leg is shorter, is associated with overall lower incidence of lower extremity running injuries. (7) There are three categories of LLD: mild = < 3cm, moderate = > 3cm but < 6cm and severe = > 6cm. The definition of a biomechanically meaningful asymmetry differs amongst orthopedic specialists. (8) Mild differences have not been convincingly linked with any specific pathologies but moderate and severe have been linked to structural deformities and functional impairments. (8). Most LLD are associated with stress fractures of the longer limb, which decreases the amount of energy that can be absorbed as well as output of force. The stress fracture can also lead to muscle weaknesses from the hip down to muscles of the foot and can also decrease the force of muscle pull on the bone to keep runners from exceeding threshold stress. Although runners can still be quite functional with mild LLD, it is still important to monitor symptoms and adjust loading as necessary to avoid injuries such as stress fractures. (8)
Back problems: The pelvic tilt caused by a leg length inequality (LLI), when one leg is shorter, may invoke a functional scoliosis in runners, which is a transient phenomenon caused by concavity of the side of the longer limb. Although it is unknown whether or not this transient functional scoliosis will become structural over time, it can be hypothesized that the LLI can be a causative factor in the development of low back pain while running. (9) Some other potential low back injuries that can be caused by LLI are: tight musculature on side on concavity (QL, paraspinals, latissimus dorsi) as well as weakness and muscle imbalance of the same muscles on the contralateral side of the body. At the joint level, subjects with LLI can have sciatica and compression of the disc and annulus, which can refer pain down the leg or alter pain, temperature, and other sensations such as vibration, pressure and proprioception depending on which part of the nerve is being compressed. Maintaining leg symmetry can be important to help prevent low back pain in runners. (9)
Single Leg Balance as Determinant of Symmetry
Single leg balance can be assessed by comparing balance while standing on one leg to the other leg. This test can adjusted to the runner’s skill by closing the eyes or standing on a compliant surfaces (such as a pillow or rolled towel) which will increase the difficulty of the task. Videoing your performance may be able to show you variances between your left and right leg that you may not notice by “feel.” The BioSway posturography platform can show small variances in postural sway to a very accurate amount. According to a study by Hatton, single leg balance is shown to be a good determinant of leg symmetry. (5)
Exercises to Improve Single Leg Balance
(goal: perform exercises that promote balance on “weaker” leg)
Stand on one leg eyes open
Stand on one leg eyes closed
Stand on one leg on foam eyes open/close
Jump rope skipping on leg (what is this called)
Exercises to Improve Symmetry in Leg Strength
(goal: perform exercises that bias one leg to prevent dominance compensation)
Knee locking/unlocking 20 degrees
Single leg partial squat
Theraband hip exercises while standing on one leg
Leg asymmetries have been linked to various problems in the back, hip, knee, and ankle. These asymmetries can be in the form of strength, leg length discrepancy, coordination of movement, and balance being different between the left and right legs. Performance, even in elite athletes, can be unaffected by these asymmetries. That means, athletes can continue to compete at high levels with good success despite interlateral leg asymmetries due to the body’s amazing ability to compensate for these differences. However, with long distance running, the cumulative effects of running a marathon on muscle fatigue, endurance, and preexisting injuries can mitigate the body’s ability to compensate, and can lead to chronic injuries in the long term. Research supports addressing these asymmetries with exercise and physical therapy, especially in the long distance running population and those with chronic leg problems.
- Zifchock RA, Davis I, Hamill J. Kinetic asymmetry in female runners with and without retrospective tibial stress fractures. J Biomech 2006;39(15):2792-2797.
- Zifchock RA, Davis I, Higginson J, McCaw S, Royer T.. Side-to-side differences in overuse running injury susceptibility: a retrospective study. Hum Mov Sci. 2008;27(6):888-902.
- Radzak KN, Putnam AM, Tamura K, Hetzler RK, Stickley CD.. Asymmetry between lower limbs during rested and fatigued state running gait in healthy individuals. Gait Posture. 2017;51:268-274.
- Ciacci S, Michele RD, Fantozzi S, Merni F. Assessment of Kinematic Asymmetry for Reduction of Hamstring Injury Risk. International Journal of Athletic Therapy and Training. 2013;18(6):18-23. doi:10.1123/ijatt.18.6.18.
- Hatton AL, Crossley KM, Clark RA, Whitehead TS, Morris HG, Culvenor AG. Between-leg differences in challenging single-limb balance performance one year following anterior cruciate ligament reconstruction. Gait Posture. 2017 Feb;52:22-25. doi: 10.1016/j.gaitpost.2016.11.013. Epub 2016 Nov 11.
- Pappas P, Paradisis G, Vagenas G. Leg and vertical stiffness (a)symmetry between dominant and non-dominant legs and young male runners. Hum Mov Sci. 2015;40:273-283.
- Gent R, Middlekoop M, Os A, Bierma-Zienstra S, Koes B. Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review. Br J Sports Med 2007;41:469-480.
- McCaw S, Bates B, Eng B. Biomechanical implications of Mild Leg Length Inequality. British Journal of Sports Medicine 1991; 25(1) 10-14.
- Azizan A Basaruddin K, Salleh A. The Effects of Leg Length Discrepancy on Stability and Kinematics-Kinetics Deviations: A Systematic Review. Applied Bionics and Biomechanics 2018; Article ID 5156348: 22 pages.