#72 - Tendons: from exercise adaptation to injury and rehabilitation, with Professor Michael Kjær
Nov 12, 2023
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Professor Michael Kjær, an expert on tendons and exercise, discusses various topics including tendon injuries, prevention and treatment, muscle-tendon interactions, factors that determine injury vulnerability, autophagy and mitophagy in maintaining muscle and tendon health, tendonopathy and potential treatments, shockwave therapy for calcifications, collagen supplementation, secretion of molecules by tendons during exercise, influence of circadian rhythm and sleep on tendons.
Muscle and tendon injuries can be classified into acute injuries and overuse injuries, with acute injuries occurring when the load exceeds the capacity and overuse injuries resulting from prolonged or repetitive stress.
In the early stages of overuse injuries, tendons may exhibit water accumulation and swelling, accompanied by an increase in certain molecules. Over time, structural changes occur, but the core fibers of the tendon remain intact.
Chronic tendon pain occurs when overuse injuries persist, leading to tissue changes and scar tissue deposition. Pain does not necessarily indicate a rupture, but continuing to train with pain can prolong recovery.
Controlled loading through exercises like calf raises is effective for stimulating tendon healing and adaptation. Stretching alone does not significantly decrease the risk of tendon injury.
Deep dives
Types of Muscle and Tendon Injuries
Muscle and tendon injuries can be classified into acute injuries, such as ruptures or strains, and overuse injuries that primarily affect the tendons. Acute injuries occur when a load on the muscle or tendon exceeds its capacity, while overuse injuries result from prolonged or repetitive stress. The exact factors determining why a muscle or musculotendinous junction is affected versus the tendon alone are not yet fully understood.
Water Accumulation and Dynamic Changes in Tendons
In the early stages of overuse injuries, tendons may exhibit water accumulation, leading to swelling. This water accumulation is often accompanied by an increase in certain molecules that attract water. Over time, structural changes occur, such as the in-growth of blood vessels and nerves, as well as the deposition of scar tissue. However, the original core fibers of the tendon still remain intact, and the dynamic turnover of connective tissue proteins plays a role in maintaining tendon health.
Chronic Tendon Pain and Healing Process
Chronic tendon pain typically occurs when overuse injuries persist for months, resulting in tissue changes within the tendon. This prolonged duration of injury may lead to delayed healing and the presence of scar tissue, making recovery more challenging. It is essential to note that pain in a tendon does not necessarily indicate an impending rupture. However, continuing to train with pain can potentially lengthen the recovery process and exacerbate the condition.
Blood Flow and Vascularization in Tendons
Tendons have relatively limited blood flow compared to muscles, but they do contain some vessels. The exact role and significance of increased blood flow and vascularization in overuse injuries are still being investigated. While hypervascularization is often considered a diagnostic sign of overuse injuries, it's important to note that elite athletes may also exhibit increased blood flow in their tendons without experiencing severe symptoms.
The importance of exercise in tendon health
Exercise plays a crucial role in maintaining tendon health. Top athletes who have a lot of blood flow and vessel changes in their tendons may be more prone to problems in the future, but not all of them experience issues. Blood flow and vessel changes may not necessarily indicate a problem in the tendon, but rather a response to training. Resting alone is not recommended as it can cause a decrease in turnover and slow down regenerative processes. Controlled loading through exercises like calf raises can help stimulate tendon healing and adaptation.
The role of controlled loading in tendon healing
Controlled loading, such as performing calf raises, is an effective approach for enhancing tendon healing and adaptation. It is not necessary to perform intense eccentric exercises, as both concentric and eccentric contractions can yield positive results. Maintaining flexibility is important, especially for sports that require a higher range of motion. However, stretching alone does not significantly decrease the risk of tendon injury. Warm-up exercises, on the other hand, have been found to have a positive impact on performance but do not play a major role in preventing injuries.
The impact of age and risk factors for tendon injury
As people age, tendons generally experience reduced turnover and may become stiffer if not regularly exercised. However, age alone does not significantly increase the risk of tendon injuries. Factors such as training intensity, sudden increases in training load, and repetitive explosive movements contribute more to the likelihood of tendon injuries. The presence of certain risk factors, such as high-velocity muscle contractions and genetic predispositions, can also affect the risk of injury. Adequate rest, variation in training, and paying attention to warning signs can help prevent tendon injuries.
Dr Glenn McConell chats with Professor Michael Kjær from the Department of Clinical Medicine, Bispebjerg Hospital, the University of Copenhagen, Denmark. He is an expert on tendons and exercise. We chatted about muscle vs musculotendinous junction vs tendon, what structures get injured and why, tendon injuries: mechanisms, prevention, treatment, acute vs chronic/overuse tendon injuries, best to rest or exercise injured tendons?, whether diet, supplements or medicine can assist recovery from tendon injuries etc. We also discussed his earlier work on glucose metabolism during exercise. A very interesting chat. 0:00. Introduction 2:05. How Michael got into exercise research 5:54. His glucose metabolism during exercise work 11:20. Redundancy in physiology, animal vs human work 13:45. His muscle work and movement into injury research etc 16:20. His move into connective tissue/tendon research 21:30. Taking a risk to move fields/finding collaborations 23:30. Muscle vs musculotendinous junction vs tendon 28:00. Why get muscle/tendon injuries 31:45. Tendon stretches as muscle shortens 33:05. Age and body weight effects on injury 34:15. Interface between muscle and tendon 37:10. Tendon overuse injuries 41:40. What determines if injury occurs in muscle vs tendon 44:20. Why tendon can feel better once warms up 46:45. Water accumulation vs structural changes 48:00. No evidence that exercising painful tendon increases rupture 50:00. Development and turnover of tendons/circadian rhythm 52:08. Blood vessels and flow in tendons at rest/during exercise 55:00. Strength training and tendon size 56:20. Best not to rest if injured tendon 57:45. Need controlled loading of tendon to recover 1:00:00. Supplements/surgery for tendon recovery? 1:01:00. Can a tendon biopsy activate tendon repair? 1:02:40. 3 x 10 reps per week may be enough 1:04:50. Don’t need to focus on eccentric phase 1:06:35. Need good shoes etc to reduce injury? 1:09:00. What is a tendonopathy? 1:10:00. RICE, anti inflammatories and cortisol shots etc? 1:13:01. Collagen etc supplements and tendons 1:15:10. Prevention of tendon injuries 1:17:40. Signs of tendon injury 1:20:20. Does warm up/ stretching reduce injury? 1:23:18. Can a tendon torn off the bone recover without surgery? 1:24:10. Age and tendon stiffness: inactivity vs age 1:25:50. Fast twitch fibers and injuries 1:27:35. Type 2 diabetes and tendon problems 1:28:35. Can predict tendon injuries? 1:29:18. Do tendons secrete molecules during exercise? 1:30:00. Circadian rhythm, sleep and tendons 1:32:17. Takeaway messages 1:33:28. Outro Inside Exercise brings to you the who's who of research in exercise metabolism, exercise physiology and exercise’s effects on health. With scientific rigor, these researchers discuss popular exercise topics while providing practical strategies for all. The interviewer, Emeritus Professor Glenn McConell, has an international research profile following 30 years of Exercise Metabolism research experience while at The University of Melbourne, Ball State University, Monash University, the University of Copenhagen and Victoria University. He has published over 120 peer reviewed journal articles and recently edited an Exercise Metabolism eBook written by world experts on 17 different topics (https://link.springer.com/book/10.1007/978-3-030-94305-9). Connect with Inside Exercise and Glenn McConell at: Twitter: @Inside_exercise and @GlennMcConell1 Instagram: insideexercise Facebook: Glenn McConell LinkedIn: Glenn McConell https://www.linkedin.com/in/glenn-mcconell-83475460 ResearchGate: Glenn McConell Email: glenn.mcconell@gmail.com Subscribe to Inside exercise: Spotify: shorturl.at/tyGHL Apple Podcasts: shorturl.at/oFQRU YouTube: https://www.youtube.com/@insideexercise Anchor: https://anchor.fm/insideexercise Google Podcasts: shorturl.at/bfhHI Anchor: https://anchor.fm/insideexercise Podcast Addict: https://podcastaddict.com/podcast/4025218 Not medical advice
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