Simple Exercises That Can Repair Tendons, Isometrics vs. Eccentrics, and More — Dr. Keith Baar

Here are the top 10 key takeaways from Dr. Keith Baar's insights on tendon healing, proper exercise, and rehabilitation.

1. Isometric exercises are superior to eccentric exercises for tendon healing

Isometrics involve holding a position without movement, which allows load to be distributed evenly throughout the tendon. This even distribution is crucial because tendons have strong and weak parts. During dynamic movements, the strong parts shield the weak parts from stress (called "stress shielding").

When you hold an isometric position, the strong parts eventually fatigue, allowing stress to reach the weaker portions that need it for healing. Dr. Baar explains that the standard recommendation of eccentric exercises (like slowly lowering weights) works not because of the eccentric nature, but because of the slow velocity. Isometrics, with zero velocity, provide the optimal loading pattern for healing tendons.

2. Ten minutes of targeted isometric loading is sufficient for tendon adaptation

Dr. Baar's research with engineered ligaments showed that tendons receive maximum stimulus within just 10 minutes of proper loading. Additional exercise beyond this timeframe adds unnecessary wear and tear without additional benefit. This is compared to a teenager who listens for 5-10 minutes before tuning out.

For optimal results, this 10-minute loading session can be done twice daily with at least 6-8 hours between sessions. This allows time for the tendon cells to recover and respond to the next stimulus. The approach has been validated through extensive research, with rock climbers showing dramatic strength improvements using these principles.

3. The optimal isometric hold duration depends on injury status

For healthy tendons, 10-second holds are sufficient to generate adaptation. However, for injured or chronically damaged tendons, longer 30-second holds are recommended. This difference exists because chronically injured tissues have stronger stress-shielding mechanisms that take longer to fatigue.

Dr. Baar's research found that stress relaxation in tendons follows an exponential curve. By the 30-second mark, tendons have reached about 85% of their maximum relaxation state. Extending beyond this to two minutes only provides about 15% additional benefit, making 30 seconds the sweet spot for efficiency in rehabilitation.

4. Beginning rehabilitation immediately after injury accelerates recovery

Contrary to common medical advice advocating rest after injury, Dr. Baar recommends starting gentle isometric loading as soon as the day after injury or surgery. His research shows that patients who begin loading two days after injury recover 25% faster than those who wait nine days.

This approach directly challenges the standard RICE protocol (Rest, Ice, Compression, Elevation) and the use of immobilizing boots. Dr. Baar points out that boots are "mechanical stress shielders" that can actually promote scarring by preventing proper loading. Even with surgical repairs, gentle isometrics in safe positions can promote better healing without compromising the surgical work.

5. Proper loading promotes healthy collagen formation rather than scarring

When tendons don't receive appropriate mechanical loading, they form scar tissue characterized by smaller, disorganized collagen fibers and excessive cell proliferation. Dr. Baar cited research by Professor Hayashi who demonstrated that preventing load on a healthy tendon quickly resulted in scarring.

Appropriate isometric loading provides the mechanical signal that directs collagen to form in an organized, functional pattern aligned with the direction of force. This directional organization is crucial for tendon strength and function. Without it, the body produces a chaotic arrangement of collagen fibers that lacks the structural integrity of healthy tissue.

6. Women have different tendon properties due to hormonal influences

Estrogen significantly impacts tendon stiffness throughout the menstrual cycle. Dr. Baar's research shows that estrogen inhibits lysyl oxidase, an enzyme responsible for cross-linking collagen fibers. These cross-links are what give tendons their stiffness.

This hormonal effect helps explain why women are 4-8 times more likely to rupture their ACL but 80% less likely to experience muscle pulls compared to men. The cyclical nature of estrogen in women means tendon stiffness fluctuates throughout the month, which has performance and injury implications. Evolutionarily, this mechanism likely developed to facilitate childbirth by allowing more tissue flexibility.

7. Overcoming isometrics are safer than yielding isometrics for rehabilitation

Dr. Baar distinguishes between two types of isometric exercises: overcoming isometrics (pushing against an immovable object) and yielding isometrics (holding a weight in position). Overcoming isometrics are preferred for rehabilitation because they allow for precise control of force development and reduction.

With overcoming isometrics, you can gradually build force over several seconds, hold for the prescribed duration, and then gradually reduce force. This careful approach minimizes "jerk" (the rate of change of acceleration), which is a primary cause of tendon injury. For injured tendons, Dr. Baar recommends developing force over 3-5 seconds, holding for 30 seconds, and releasing over 3-5 seconds.

8. Collagen supplementation can support tendon healing when properly timed

Taking hydrolyzed collagen (15-20g) with vitamin C (200-250mg) about 30-60 minutes before loading exercises can enhance tendon healing. The collagen provides necessary amino acids (particularly glycine and proline) that are used as building blocks for new collagen synthesis.

Dr. Baar recommends choosing collagen derived from animal skin rather than bone sources to avoid potential heavy metal contamination. The vitamin C is essential as a cofactor for the enzymes involved in collagen synthesis. This nutritional strategy works best when combined with the mechanical stimulus of isometric exercise, which directs where and how the new collagen is formed.

9. Common medications can significantly increase tendon rupture risk

Some widely prescribed medications dramatically increase the risk of tendon injuries. According to Finnish research cited by Dr. Baar, fluoroquinolone antibiotics (like Cipro) increase Achilles tendon rupture risk by 3.5 times. Even more concerning are angiotensin receptor inhibitors, commonly used for blood pressure, which increase rupture risk by 7.6 times.

This elevated risk has significant implications for exercise recommendations for millions of Americans taking these medications. Dr. Baar points out the irony that while these medications may reduce cardiovascular risk, they could indirectly increase it by making exercise more dangerous and less accessible. This highlights the need for a more holistic approach to health management.

10. Load is a natural anti-inflammatory that's better than ice or medication

Rather than using ice or anti-inflammatory medications after injury, Dr. Baar recommends gentle isometric loading to reduce inflammation naturally. Light isometric contractions help pump fluid out of the injured area, reducing swelling and pain without blocking the inflammatory processes necessary for healing.

For a sprained ankle, for example, Dr. Baar recommends alphabet exercises (tracing letters with the foot) immediately after injury instead of rest and ice. This gentle movement helps manage swelling while maintaining the beneficial aspects of inflammation that signal tissue repair. The approach recognizes that inflammation is a necessary part of the healing process that should be managed rather than eliminated.