As many rounds as possible in 20 minutes:
20 Box jumps, 24″ (20″)
30 Double unders
Post rounds to comments and BTW.
Jumping. We do a lot of it. Probably not as much as kids do on a daily basis, but we definitely have a fair amount of jumping and landing in CrossFit. In box jumps, double unders, olympic lifting, etc. because it’s important for improving coordination, balance, strength, power, speed, agility, accuracy, and agility. So you could say its good for us. It’s necessary, it’s functional and shouldn’t be avoided as we grow older. Often times chronic pain and injuries have developed from years and years of consistent loading and pounding on our joints and tissues, so we hear to “go swimming” or get on an elliptical to decrease that high impact. Fact is in generally healthy and well-nourished people, 15-24 weeks of progressive training is long enough to remodel and harden bones into well adapted force-transmitting machines.
A New York Times article, “Why High Impact Training is Good for Your Bones” 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.
Recently researchers at the University of Bristol gathered male and female adolescents — the body accumulates bone mass rapidly at this time of life — and had them go about their daily routines while they wore activity monitors. The bone density of the volunteers’ hips was also measured.
A week later, the scientists reclaimed the monitors to check each teenager’s exposure to G forces, a measure of impact. Those who experienced impacts of 4.2 G’s or greater — though these were infrequent — had notably sturdier hipbones. Additional work done by the same researchers showed that running a 10-minute mile or jumping up onto and down from a box at least 15 inches high was needed to produce forces that great. The significance of these findings is that people should probably run pretty fast or jump high to generate forces great enough to help build bone.”
Bone remodeling and the formation of additional bone can modify the strength of bone in direct response to the amount of stress that is applied to it. Stress to the bone increases osteoblast activity in the bone tissue. A removal of stress decreases osteoblast activity. Stress is defined as load bearing, so does it feel heavy? If yes then you might be able to call it stress. So you should be gradually getting stronger and adding weight, eating your veggies and gradually increasing the consistency and intensity of your loading, aka jumping abilities.
Train your bones with proper technique and intensity and you can avoid serious potential injuries. Our bones can change shape and density over time to adapt to our changing lives and activities. Then we can catcall across the gym about “those amazing femurs on you or wow, look at that humerus!” Don’t avoid high impact activities, just be smart about them and gradually improve them. If you haven’t already, start today.