High Impact Exercises: A Closer Look

I recently came across another NY Times article published a couple of months ago entitled "Why High-Impact Exercise is Good for Your Bones." In the first three paragraphs, writer Gretchen Reynolds states:

• "Bones should be jarred, for their own good."
• "Past experiments have definitively established that subjecting bones to abrupt stress prompts them to add mass or at least reduces their loss of mass as people age."

Ms. Reynolds then goes on to describe recent research conducted at the University of Bristol in which adolescents wore activity monitors to measure G force exposure and subsequent impact on bone mass density (BMD). She summarizes the significance of the research by stating "that people should probably run pretty fast or jump high to generate forces great enough to help build bone."

I find that I mention New York Times articles quite a bit with a sense of contrarianism, particularly from the Health & Wellness section but only because I often find that cited research is often misinterpreted or overgeneralized. These articles have a wide-reaching audience and as a physical therapist in New York City patients have often asked me if I've read them or if I implement their principles. While there is some truth behind points mentioned in these articles, one should take a closer look at the conclusions drawn from the research cited.

My biggest issue with the article is the blanket statement of high-impact exercises being good for your bones. According to the article people may incorrectly assume that aggressive aerobic activity or large volumes of plyometric exercise are valid ways of safeguarding your joints against cartilage damage or fortifying your skeleton. Yes, in the correct context, being able to endure high-impact exercises can be good for your health but not in the absence of adequate muscular strength to stabilize joints during dynamic athletic movements. To me, the article appears to prescribe "pound[ing] the ground", sprinting, hopping, jumping off and on 15" plyo-boxes and even hopping in place as measures to increase BMD and strengthen the body. There is no mention of safe, progressive, resistive strength training for the lower extremities anywhere in the article. 

The Times article appears to be another example of taking a research article or basic tenet of science such as Wolff's Law (bone gets adaptively stronger as gradual loads are placed upon it) and over-drawing conclusions from them, not unlike the topic I tweeted about yesterday mentioned in this editorial (also from the Times). The research study cited, while not bad in and of itself, is hardly strong enough evidence to validate the endorsement of "jarring bones for their own good" or to insinuate that all impact is inherently nourishing to bone. Granted, Ms. Reynolds does include disclaimers here and there to state that a physician should be consulted before engaging in such activity and that the modes of impactful exercises listed should be reserved for "young and healthy adults." But even in the absence of pain, a young and healthy individual runs the risk of developing injury if he/she lacks appropriate muscular strength to tolerate repeated impact.

A recent Men's Health article containing input from highly-regarded physical therapist Mike Reinold and strength coach Mike Boyle does a great job offering alternative exercise approaches towards preserving strength and protecting the body.

The human body can positively or negatively adapt to the stresses placed upon it. Load the body responsibly and progressively and it will get stronger. Introduce a load that the body is not prepared to handle and that stress can be the harbinger of pain and compensatory dysfunctional movement--ultimately the total opposite of what you want.