The quest for body symmetry is something that a number of medical and fitness professionals over-emphasize in their treatment or exercise program design. For example, in the National Academy of Sports Medicine’s Corrective Exercise Specialist manual, “abnormal” gait movement patterns, such as hip hike and excessive pelvic rotation, are indicators that certain muscles are “weak.” Depending on the subject’s movement dysfunctions, certain corrective exercises are recommended to “fix” the asymmetry. However, current research and evidence on human gait patterns suggest that some leg and hip asymmetry may not need to be “corrected.”
A recent research study from The Ohio State University that was published in Gait & Posture in June 2014 found a rather surprisingly prevalence of hip and knee joint moment asymmetry among healthy subjects with no pain. Among 182 “healthy, pain-free subjects,” over half of them had more than 10 percent asymmetry in hip and knee flexion and adduction moments during a walk test. (A “joint moment” is a force acting at a distance from the joint center and tending to induce rotation about the joint.) The subjects were ranged in age from 20 to 60 years, ranged in body composition from healthy BMI to obese, and ranged in activity level from sedentary to competitive athlete.
While the study did not address or investigate whether or not leg and hip asymmetry is associated with pain, lead researcher Rebecca Lambach, Ph.D. from The Ohio State University’s Mechanical and Aerospace Engineering department told Guardian Liberty Voice that the researchers observed a presence of joint moment asymmetry in the absence of pain. The study does not address stride length, step length, time, joint angles, or leg length discrepancy.
“Marker-based motion capture and force plate data were collected while subjects walked overground in their own shoes,” Lambach explains the experiment’s setup. “Force plates were embedded in the floor in the middle of a 10-meter walking path to record ground reaction forces. Data were collected at separate universities: one at Ohio State and the other at Stanford, with slightly different techniques.” Although both laboratories used at least eight high-speed motion capture cameras and at least one force plate fixed on the floor, “left and right leg data were collected from consecutive foot strikes on adjacent force plates within the same trial” per subject at Ohio State while Stanford used separate walking trials for the left and right legs.
Lambach also pointed out that a “clinically relevant value of joint moment asymmetry” has not yet been well-defined or established. “Since 10 percent has been used as a cutoff for clinically relevant differences by physical therapists during strength and performance based testing, we chose this a starting point, but clinical significance in joint moments may be different.”
Current research indicates the reliance of gait analysis or assessment to evaluate the quality of movement is pretty mixed. A systematic review published in Gait & Posture in March 2011 identified 240 studies that were qualified for analysis and showed various levels of quality of evidence, ranging from low to high. A lack of any randomized controlled trial may make gait analysis seem less reliable and valid, however, the researchers noted that current evidence tends to point out that gait analysis is effective in helping clinicians make better treatment options and improving patient outcomes. The study mentions that further research is needed to “investigate the higher levels of efficacy.”
Leg and hip asymmetry may not always need to be corrected since the nature of the asymmetry may stem from beyond the biomechanics of movement. For example, a study of stroke patients from the Heart and Stroke Foundation Centre for Stroke Recovery in Toronto, Canada, showed that “damage to the posterolateral putamen was associated with temporal gait asymmetry.” Thus, any damage to the brain and the nervous system can alter how one moves. Another study from Aalborg University in Denmark showed that pain can change a person’s postural stability, which could most likely be an adaptation and response to pain. In other words, pain is the cause of postural change, not always the other way around.
So what can health professionals glean from the Ohio State and Stanford joint study? “When an individual injures a single limb, or is diagnosed with unilateral pathology, the opposing limb is often used as a standard of rehabilitation or as a measure of comparison for determining the level of impairment of the involved limb,” Lambach said. “If symmetry is to be used for diagnosis of pathology or for measuring the success of rehabilitation, it is important to be aware of how much ‘asymmetry’ is considered ‘normal’ in healthy, pain-free individuals. In our study, we found higher than anticipated asymmetry in the knee joint moments and hip joint moments of healthy individuals. Our work suggests that joint moment asymmetry can be present in the absence of pain and pathology. Additional work is necessary to determine whether there is a threshold value of joint moment asymmetry above which pain or pathology more commonly occurs, or if there is any relationship between joint moment asymmetry and the likelihood of the development of pain or pathology over time.”
Lambach cautioned that the absence of pain in those with leg and hip asymmetry does not always mean that there is nothing “wrong.” “Based on our investigation, we cannot say whether or not there is a correlation between joint moment asymmetry and pain or pathology. None of our subjects had current or consistent lower extremity pain at the time of data collection. It is not safe to assume that the two are not correlated simply because the subjects in this study had higher than expected joint moment asymmetry and yet were healthy and pain-free. Additional research involving patients who are experiencing pain would be necessary in order to test for associations between asymmetry and pain.”
Perhaps, as researchers and clinicians gain a better understanding of movement, pain, and behavior, the obsession with nit-picking and “fixing” every asymmetry in clients’ or patients’ movement patterns can be toned down. Therefore, leg and hip asymmetry do not always need to be “corrected.”
By Nick Ng