How a Subtle Evolutionary Adaptation to Bipedality has Increased the Likelihood we will Fracture our Hip as We Get Older, and What We Can Do to Prevent it.
Last year, 300,000 Americans fractured their hip after falling. The long-term consequences of hip fractures are devastating as nearly 25% of the people who fracture their hip will be dead in one year, and 50% of them will be unable to return to their prior level of function.
Although a hip can fracture with a fall in any direction, more than 75% of all hip fractures are the result of a sidewards fall, in which the person falls and lands directly on the outer side of their hip.
Until recently, it's been unclear as to why lateral falls are so destructive, as people in their twenties do not break their hips when they fall sidewards. In contrast, hip fracture rates increase 100-fold in 60 year olds and 1,000-fold in 80 year olds.
When our ancestors first started walking around on 2 legs, the weight of the upper body produced almost equal tensile and compressive bending strains on the femoral neck (A and B). Due to the magnitude of these bending forces, the femoral neck would fracture pretty quickly if our ancestors attempted to walk long distances on a regular basis.
To deal with the changes in stress associated with being upright, our femoral necks angled up more and our greater trochanters moved outwardly. These changes produced a redistribution of tensile and compressive forces (dotted and straight arrows) which reinforced the lower femoral neck, making it better able to tolerate the forces of being upright. Unfortunately, this redistribution of bending strains left a weak spot in the upper outer femoral neck (C).
BECAUSE PEAK BONE DENSITY OCCURS WHILE YOU'RE IN YOUR EARLY TWENTIES, YOU SHOULD BEGIN THESE EXERCISES EARLY IN LIFE, AS EVEN THOUGH IT IS POSSIBLE TO PREVENT ADDITIONAL BONE LOSS IF YOU START EXERCISING WHEN YOU'RE OLDER, IT IS DIFFICULT TO REVERSE OSTEOPOROSIS WITH EXERCISES ALONE, AS IT CAN TAKE DECADES TO APPRECIABLY INCREASE BONE DENSITY IN THE FEMORAL NECK WITH EXERCISE INTERVENTIONS.
When we fall on our sides, the higher femoral neck angle allows body weight to create a bending force that compresses the weak spot in our femoral neck.
This produces a compression fracture in the upper femoral neck, which is quickly followed by a tensile fracture in the lower femoral neck.
Mayhew et al. (2) claim that unlike walking and running, exercising while your hips are flexed specifically strengthens the upper femoral neck, which can prevent age-related fractures with lateral falls. The authors support their statement by noting that in cultures where people squat for long periods of time with their hips flexed, like rural China and Gambia, there is a very low incidence of hip fractures,
even with lateral falls, despite a significantly higher prevalence of osteoporosis in these
societies. The authors state that it is also possible to strengthen your hips with stationary bike riding, rowing, jumping and/or stairclimbing .
The deep hip external rotator muscles attach directly on of the weak spot in the femoral neck. One possible mechanism is that squatting activates the deep hip external rotators, which attach around the weak spot in the femoral neck. It's been known for decades that when muscles contract, they pull on their bony attachment points with a significant amount of force, which in turn can strengthen that specific spot. It is also possible that these exercises produce a torque on the femoral neck itself, which accelerates bone remodeling. Either way, strengthening exercises performed with the hips flexed can significantly reduce the rate in which our bone density decreases over time, and can even prevent sidewards falls as hip strengthening exercises have been proven to enhance lateral stability.
The best hip and knee strengthening exercises. A) Fencer's lunge with rubber medicine ball: To do this exercise, stand in a forward lunge position while holding a rubber medicine ball. Next, pivot forward at the hips while maintaining a straight spine and move the ball forward as far as possible. You should not move so far forward that you lose balance and hold this position for three seconds before returning to the start position. B) Sidelying hip rotator exercise: While resting on your side, raise and lower the ankle (arrow) with the hip and knee flexed 90° C) Curtsy step up: While standing on one leg on a 6-inch step, move the opposite leg down and back (arrow) as you lean forward. At first you will need to stabilize yourself with one hand while the opposite hand holds a weight.
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Reposted from humanlocomotion.com
Dr. Michaud