How Does Gravity Affect Your Bones?

What is the difference between you and an astronaut living in space when it comes to your bones? Guessed it yet? G-R-A-V-I-T-Y! That is the primary difference! Though they may have a slightly different diet and consume their meals differently, their nutrition has the same intent – to provide the body with the nutrition it needs to provide what each needs to live. While they may have a difference in form, the idea is the same… to fuel your body with what it needs to sustain you and maintain the best health possible.

Thanks to the advancement of the space programs, we have found some basic differences between how an astronaut lives and how we live, and the primary difference between living in space and living on Earth is that there is no gravity in space. This should help us better understand what is needed when it comes to addressing bone health. Scientists have learned that astronauts living in space, even for just a few months, lose bone density. Why? Again, gravity is the difference, or in their case, the lack thereof.

In other words, to have and maintain the best bone density we can have is to be in a gravity field that puts weight on our bones or to “add” to that gravitational force. The good news for us is we have that.

On Earth, gravity continuously loads weight-bearing bones (spine, hips, pelvis, legs), stimulating bone remodeling that maintains density and strength. In microgravity, that mechanical loading largely disappears, so bone resorption (breakdown) outpaces formation, causing rapid loss of density and strength—especially in those same weight-bearing sites. ¹

Astronauts typically lose about 1–1.5% (sometimes up to ~2%) of bone mineral density (BMD) per month in the hip and spine during missions of several months. This is roughly 10 times faster than typical age-related loss on Earth (e.g., ~0.5–1% per year in older adults or postmenopausal women). Losses are greatest in the lower limbs, pelvis, and lumbar spine; non-weight-bearing bones (e.g., arms/radius, skull) show little loss or even slight gains. Trabecular (spongy) bone is particularly affected, and some microarchitectural connections can be permanently disrupted. Calcium released from bone also raises the risk of kidney stones. ²

Modern countermeasures on the International Space Station (ISS) substantially reduce but do not always eliminate the loss:

• Intensive daily exercise (~2–2.5 hours), especially high-load resistance training on the Advanced Resistive Exercise Device (ARED, up to ~600 lb force for squats, deadlifts, etc.), combined with treadmill running (with harness for loading) and cycling.
• Nutrition: adequate calories/protein to maintain body mass, calcium, and vitamin D (typically 800 IU/day supplementation).

After the return to Earth, recovery is incomplete for many astronauts, especially after longer missions (>~6 months). Bone formation markers rise, and resorption falls, with the most active recovery window in the first ~6 months. On average, only about half the lost strength/density is regained after 1 year; residual deficits (e.g., ~1–2% or more in tibia BMD/strength) can equate to a decade or more of normal aging-related loss, and some trabecular microarchitecture changes appear permanent because disconnected structures cannot fully reconnect—remaining bone may thicken instead. Longer missions predict poorer recovery; some individuals fully recover (or nearly so) with good countermeasures and rehab, while others retain lasting changes. Full recovery of density or microarchitecture can take years in some cases, or may remain incomplete. ³

Post-flight compensation focuses on:

• Progressive, supervised rehabilitation and continued high-intensity resistance/weight-bearing exercise (plus aerobic activity) under gravity to stimulate reloading and remodeling.
• Ongoing nutrition support (vitamins/minerals, adequate protein/calories).
• Medical monitoring (High-resolution imaging, bone turnover markers) for years, sometimes as part of lifetime astronaut health surveillance.
• Nutrition has remained the primary method of compensation

While these measures may help restore function and minimize fracture risk, the best thing those who live on the Earth can do is to maximize what is used in compensating: Increased nutrition (which needs to be sourced from food and sound nutrition, including the avoidance of as many antinutrients in the diet), and targeted weight-loading exercises to put a load on the bones to simulate bone growth through new osteoblasts.

Exercises:

Bones strengthen in response to mechanical loading (weight-bearing forces, muscle pull, and impact) that stimulate osteoblasts to build denser, stronger tissue—especially at sites like the hips, spine, and legs that lose density fastest in microgravity or with aging/disuse. Progressive overload (gradually increasing challenge) is key, similar to the high-load resistance work astronauts perform on devices like the ARED. ⁴

Progressive Resistance Training (Most Targeted for Bone)

Perform these 2–3 non-consecutive days per week. Aim for 2–3 sets of 5–12 repetitions at a challenging intensity (roughly 70–85% of what you can lift once, or hard effort where form remains solid). Focus on compound movements that load the spine and hips axially.

• Squats (bodyweight → goblet with dumbbell/kettlebell → barbell back or front squat): Load the lumbar spine, hips, and legs. Keep chest up and knees tracking over toes.
• Deadlifts (hip hinge with light weight or kettlebell → Romanian or conventional barbell): Highly effective for the posterior chain, spine, and femoral neck. Prioritize hip hinge technique over heavy weight initially.
• Lunges or walking lunges (bodyweight → holding dumbbells): Target hips, legs, and balance; vary directions for multi-planar loading.
• Hip thrusts or glute bridges (bodyweight → weighted): Strong hip loading with less spinal compression.
• Overhead press (dumbbells or barbell, standing preferred): Axial loading through the spine plus upper body.
• Rows (bent-over dumbbell, barbell, or cable/band): Support posture and upper back/spine.
• Heel raises / calf raises (double-or single-leg, progressive load): Load lower legs and ankles.
• Farmer’s carries (walk while holding heavy weights at sides): Whole-body loading, grip, and core.

These mirror many of the resistance moves used in space countermeasures and evidence-based protocols (e.g., high-intensity programs like LIFTMOR elements) shown to help maintain or improve BMD at the spine and hip. ⁵

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Weight-Bearing and Impact Activities

Do these most days (aim for ~30 minutes cumulative). They provide gravitational loading and ground-reaction forces.

• Brisk walking, hiking (especially hills or uneven terrain), or stair climbing.
• Dancing, tennis/pickleball, or other multi-directional sports.
• Jumping variations (if appropriate for your fitness and bone health): jump rope, box step-offs/landings (low height), hopscotch-style hops, or controlled jump squats. Even brief bouts (e.g., 50 impacts per session in sets) can help. Heel drops are a lower-impact alternative. ⁶

Practical Tips

• Progression and form: Start with bodyweight or light resistance and master technique (consider a trainer or physical therapist, especially if new or recovering). Increase load, reps, sets, or impact gradually.
• Balance and posture: Include elements like single-leg work, bird-dogs, or controlled back extensions to improve stability and reduce fall risk.
• Frequency and recovery: Resistance 2–3×/week; impact/weight-bearing most days. Allow recovery between hard sessions.
• Combine approaches: Programs mixing progressive resistance with impact often show the strongest benefits for hip and spine density. ⁷
• Supportive factors: Pair with adequate protein, calcium, and vitamin D from food; maintain overall activity and avoid prolonged sitting.
• Safety: Consult a doctor or qualified professional before starting, particularly if you have low bone density, osteoporosis, prior fractures, joint issues, or are older/post-menopausal. Avoid excessive spinal flexion under load or high-impact if contraindicated; supervised progressive training has a good safety profile in studies even for those with low bone mass. Stop if you experience pain beyond normal muscle fatigue.

Consistency over months produces measurable benefits. These exercises not only target bone but also build the muscle strength that further loads and protects the skeleton—useful both for everyday bone health and for concepts drawn from astronaut recovery. If you have specific goals, fitness level, or equipment constraints, more tailored progressions are possible.

Nutrition/Diet

We’ll work on this more on another page, separate from this, but for now, focus on “Choosing the Right Foods for Osteoporosis”.

Remember: Healthy Bones Are Happy Bones!

This is a page from “Opening the Doors to Reversing and Healing Osteoporosis”

Copyright © Douglas K. Johnson – all rights reserved

Sources and Citations:

1. nasa.gov
2. nature.com
3. reuters.com
4. orthoinfo.aaos.org
5. https://howardluksmd.substack.com/
6. orthoinfo.aaos.org
7. springer.com

Medical Disclaimer