A real randomised trial underlies the one percent figure, but its design differs from the claim in important ways. In the Allison 2013 trial, fifty healthy, community-dwelling older men commenced a 12 month high impact unilateral exercise intervention which increased to 50 multidirectional hops, 7 days a week on one randomly allocated leg . BMD of both femurs was measured using dual energy X-ray absorptiometry before and after 12 months of exercise, by an observer blind to the leg allocation. The design was deliberately within-subject: lifestyle changes and individual variability may confound exercise trials but can be minimised using a within-subject unilateral design (exercise leg vs. control leg) that has high statistical power . The follow-up imaging study confirms the direction of effect: brief, daily unilateral hopping exercises increased femoral neck BMC in the exercise leg versus the control leg of older men, and a further analysis evaluated the effects on cortical and trabecular bone and its 3D distribution across the proximal femur using clinical CT . Across the entire proximal femur, cortical mass surface density and endocortical trabecular density increased significantly with exercise, with larger localized changes evident in some localized regions, and 12 months of very brief (approximately 3 minutes) hopping exercises produced varied and focal changes in cortical and trabecular bone throughout the proximal femur as well as changes in biomechanical properties of bone strength at the mid-femoral neck.

So the effect is real, measured at the femoral neck, over 12 months, in older adults. What it was not: 100 bilateral floor jumps, and not a mixed population of everyone over 50.

The "20 jumps is enough" element of the video traces to a different trial in a different population. Sixty premenopausal women aged 25 to 50 completed the intervention; the Jump 10 group performed 10 jumps with 30 seconds rest between jumps, twice daily for 16 weeks, while the Jump 20 group performed the same protocol but with 20 jumps, with hip BMD measured by dual-energy x-ray absorptiometry.

After 16 weeks, both jumping groups had improved hip bone density compared with women who did not jump, and the group doing 20 had done better than the group doing 10. That is 16 weeks, in women aged 25 to 50, that is, largely premenopausal and largely below the age threshold the video invokes.

Evidence in women also does not transfer cleanly. Bassey and Ramsdale found a significant increase in femoral BMD after 6 months of 50 jumps daily among premenopausal young women aged 29.8 to 32.0 years. The same research group's subsequent paper is titled "Pre- and postmenopausal women have different bone mineral density responses to the same high-impact exercise" (Bassey et al., J Bone Miner Res 1998), which on its face indicates the response is not uniform across menopausal status. I was unable to retrieve that abstract before exhausting search access, so I am not stating its numerical result here.