Dr. Mitch Broser
One major thing that sets humans apart from other animals and organisms on this planet is our ability to walk on two feet. We weren’t always this special. At one time, millions of years ago, we were 4-legged mammals designed for climbing and short-distance travel. Our species slowly evolved to become upright, bipedal endurance machines.
Part of human evolution included anatomical adaptations of our pelvis and femur to allow for double extension from the hip and spine to improve walking economy. The pelvis got shorter and wider, the femurs got longer and more vertical, and the hip joint itself changed shape and structure to allow for hip hyperextension. The gluteal and hamstring muscles also evolved to produce more strength at greater hip hyperextension to propel the body forward. The straight-legged gait substantially improved walking economy compared with non-human apes by reducing the muscle activity needed to support the body weight with each step.
Humans’ shorter and reoriented ischium resulted in a greater functional range of hip extension, enabling the hamstrings to hyperextend the hip beyond 200o (See Fig 1).
In humans, the gluteus maximus is greatly enlarged and serves a distinct and complementary role with the hamstrings powering hip extension. In human walking, hyperextension of the hip is powered in part by the hamstring and the gluteus maximus is notably quiet throughout the stance phase. Instead, the gluteus maximus is active when the hip is more flexed, such as during the early portion of stance phase during running and climbing).
The large gluteus maximus seems to compensate for pelvis morphology and the reduced effectiveness of the hamstrings when the hip is flexed (<40o), where the hamstring cannot power extension. It’s possible that gluteus maximus enlargement and complementarity with the hamstrings began in early humans. (click here to read more about the history of human evolution in Mitch’s Blog: We’re Losing it!)
While we are living in the most sedentary era to date, many people do not use their hips the way they have been designed to be used through millions of years of evolution. Instead of spending our days moving freely, we spend the majority of our waking hours seated with our hips in a stationary flexed position and very rarely extend our hips. If we don’t use our bodies the way there were designed to be used, then we will lose basic movement capacities and physical health.
There is a significant amount of research looking at hip extension, gait and their relation to joint health. Lee and colleagues (2005) found that young adults had an average peak hip extension of 11o +/- 6o, while average peak hip extension in the elderly was 7o +/-6o at comfortable walking speeds. This difference was exaggerated at faster walking speeds. This study suggested that decreased hip extension in the elderly are gait-related rather than the manifestation of postural decline. Kumar and colleagues (2015) found that people with mild to moderate hip osteoarthritis (OA), as seen on x-ray, had greater hip flexion and lower hip extension during walking compared to healthy subjects. The study suggested that a reversal in the extension motion in people with hip OA is associated with structural and symptomatic severity of hip OA and could potentially be used as indicators of OA disease status.
Having a better understanding of our basic physical needs can help us train smarter to give our bodies what they need to optimize performance and promote joint health. Can your hips extend? Do they possess the movement capacity for your training, or the basic capacity to function in your daily living. Movement exploration in Kinstretch is an opportunity to identify your movement limitations, learn about your body and take stop forward in moving better.
References:
- D. Kumar, et al. Anatomic correlated of reduced hip extension during walking in individuals with mild-moderate radiographic hip osteoarthritis. J ortho Res. 33(4) 527-534. 2015
- E. Kozma, et al. Hip extensor mechanics and the evolution of walking and climbing capabilities in humans, apes and fossil hominins. PNAS. Vol 15, no 16, p4134-4139. 2018.
- L. Lee, et al. Reduced hip extension in the elderly: dynamic or postural? Arch phys med rehabil. Vol 86 L.W. 2005