Episode Overview

Podcast: What's That Rash?
Episode: Is running bad for your knees?
Date: September 23, 2025
Hosts: Norman Swan & Mark Humphries
Main Theme:
This episode answers a common health question: does running damage your knees? Drawing on personal experience, expert interviews, and scientific evidence, hosts Norman Swan and Mark Humphries discuss whether regular running leads to knee osteoarthritis, how injuries and inflammation contribute, and what recreational runners should really worry about.

Key Discussion Points & Insights

1. Personal Knee Stories and Common Myths

• Mark’s Knee Journey:

  • Mark shares his story of knee issues stemming from a teenage bicycle accident, resulting in chronic subluxation, surgery, and early-onset arthritis.
  • Quote: "I'd be walking along and suddenly my knee would crumple under me." (01:31, Mark)
  • His experience is used to highlight that many develop osteoarthritis after injuries, not simply from wear and tear.

• Australian Context & Myths:

  • Australia (and especially South Australia) has very high rates of knee replacements, but this may be due more to medical practices and attitudes than actual rates of running.
  • An Adelaide orthopaedic surgeon once attributed high knee replacement rates to people "grinding our knee joints to sand" via exercise, but evidence for this is weak (04:17, Mark).
  • Rheumatologist Prof. David Hunter suggests much of the belief that exercise ruins knees is "mythology." (04:59, Norman paraphrasing Hunter)

2. Biomechanics and Benefits of Running

• Musculoskeletal and Metabolic Effects:

  • Running is considered beneficial: it strengthens muscles, increases bone density, and improves joint health via increased synovial fluid movement and reduced inflammation (06:15–07:45).
  • Quote: "For the everyday runner ... it's not convincing that there is any permanent damage at all to the knee." (07:13, Mark)
  • Exercise reduces inflammation and, for each kilo lost, pressure on the joints drops substantially.

• When Running Is Problematic:

  • Previous injuries (e.g., from rugby, netball) make a knee more vulnerable to long-term issues, but it’s the injury itself, not the act of running, that's the risk factor (08:17).

3. Research Evidence: How Much is Too Much?

• Elite vs. Recreational Runners:

  • Studies on elite athletes show some joint stress post-marathon, but joints recover; for non-elite runners, evidence does not support permanent damage (07:13).
  • Large, long-term studies like the Australian HALO Study favor running/exercise for long-term joint health, though definitive answers are still awaited (09:08).

• The U-Shaped Curve:

  • Risk of knee osteoarthritis is highest among the very inactive and the ultra-high-volume runners, forming a 'U-shaped' risk curve. The lowest risk is at moderate activity levels (09:35–10:06).
  • However, those on the low-activity end often have pre-existing knee issues or higher body weight, which may confound the data.

4. Osteoarthritis: More Than 'Wear and Tear'

• The Role of Inflammation:
  • Modern understanding views osteoarthritis as an immune/inflammatory condition, not just a mechanical "wear and tear" issue (11:55).
  • Quote: "It's simply not what osteoarthritis is. ... it's now known that osteoarthritis is an immune condition. It's not autoimmune, but your immune system is involved and you do get inflammation in the joint..." (12:13, Mark)
  • Metabolic factors (e.g., obesity, systemic inflammation) influence joint health as much as physical forces do.

5. What’s the "Sweet Spot" for Exercise?

• No Perfect Number, But Guidance:
  • Moderate activity—about 150 minutes of moderate exercise per week, including jogging—is unlikely to harm knees without prior injury (14:03).
  • Comprehensive leg and core strength supports knee health more than just focusing on quadriceps (16:45).

6. Genetics and Osteoarthritis Risk

• Ben’s Family History:
  • Listener Ben, a regular recreational runner, worries due to multiple joint replacements among his relatives.
  • Expert Advice: "When he’s got a family history of osteoarthritis, he’s doing the right stuff to prevent it." (16:16, Mark)
  • Regular, moderate exercise is protective—even with concerning family history.

7. Personal Pain Management and Rehabilitation

• Mark’s Approach:

  • Mark avoided knee replacements by focusing on holistic leg rehabilitation: intense cycling, progressive weight training, and Pilates (16:45).
  • The result: pain-free living despite a persistent, habitual limp.
  • Quote: "People looking at me limping think I’m in pain, but I’m actually not..." (17:50, Mark)

• Surgery:

  • Only pursue joint replacement at the point of significant pain or disability, not before.
  • Quote: "I just don’t believe in getting surgery done when you don’t need it. There’s always a complication risk..." (18:08, Mark)

Notable Quotes & Memorable Moments

• "Are we really running more than other countries?" (04:43, Norman)
• "If you want to prevent osteoarthritis, you want to do weight bearing exercise and you want a little bit of impact on the bones in order to stimulate bone growth." (07:02, Mark)
• "Exercise reduces inflammation in your body." (07:30, Mark)
• "It looks as though there may be a sweet spot." (11:21, Mark)
• "Osteoarthritis is an immune condition ... your general metabolic state can make it worse or better." (12:13, Mark)
• "If it’s inevitable, why not get [a knee replacement] earlier?" (18:04, Norman)
• "Absolutely." (18:26, Mark, on whether rehab is worth it)

Important Timestamps

• 01:24 – Mark recounts his personal knee injury and surgery.
• 03:14 – Listener Ben’s question about running and joint health is introduced.
• 04:17 – Myth: high knee replacement rates due to excessive running in Australia.
• 06:15–07:45 – The physiology and benefits of running for joint and bone health.
• 09:08 – Discussion of large studies on recreational runners (e.g., HALO Study).
• 09:35–10:42 – U-shaped curve of knee osteoarthritis risk and physical activity.
• 11:55–13:45 – New understanding: osteoarthritis as an inflammatory process.
• 14:03 – "Sweet spot" for safe exercise volume.
• 14:41 – Hand osteoarthritis as evidence that OA isn’t just 'wear and tear.'
• 16:16 – Ben’s family risk: exercise as protection.
• 16:45 – Mark’s comprehensive rehab approach and outcome.
• 18:04–18:26 – Why not do surgery early? Cautions about risk and timing.

Conclusion

Summary:
Running is unlikely to damage healthy knees—and may actually help prevent osteoarthritis, unless you've had a significant joint injury. Most of the fear around "running grinding your knees to dust" is a myth, and both metabolic health and muscle strength play crucial roles. For most people, regular moderate exercise is beneficial, and knee replacements should be reserved for those with severe, persistent pain or disability. Genetics play a role, but lifestyle trumps family fate.

Listener Advice:
Keep running, balance activity with rest, focus on full-leg strength—not just quads—and consult your doctor only if pain or disability emerges. Joint replacements are valuable but should be timed appropriately.

For more questions or to send cat pics:
thatrash@abc.net.au