How Joint Degeneration Actually Happens: Load, Range, and Time Under Tension

Joint degeneration is a leading cause of chronic pain and disability in older adults. Often described as “wear and tear,” the reality is more complex. Joints can serve us for decades under heavy use, yet over time they may deteriorate due to an interplay of biological changes and mechanical stresses. Modern research shows that factors such as mechanical load, movement range, and time under tension all contribute to how and when joints wear out. Recognizing these factors can help in preserving joint health.

At the heart of joint degeneration is the breakdown of articular cartilage – the smooth cap of connective tissue at the ends of bones. Healthy cartilage provides a nearly frictionless cushion thanks to a tough collagen fiber network and water-rich proteoglycan gel. It has no blood supply, so it relies on synovial fluid and intermittent movement for nutrition. With age, cartilage’s structure degrades: the collagen network becomes stiffer and more brittle, and the tissue loses some water content and elasticity. This makes cartilage less able to absorb shock. Compounding the problem, cartilage cells (chondrocytes) have minimal capacity to repair damage. Once the smooth surface starts to fray or crack, it tends to worsen progressively because the joint no longer glides as easily. Damaged cartilage creates more friction and uneven pressure, which then accelerates wear on the remaining tissue. Other joint structures also play a role: degeneration of the menisci (cartilage pads) can expose the joint surface to higher impact, and changes in the underlying bone or joint lining often accompany cartilage loss. Osteoarthritis is now understood as a “whole joint” disease involving cartilage loss, changes in the underlying bone, and inflammation in the joint lining. Aging amplifies all of these factors, creating an environment where even normal daily forces can start to overwhelm a joint’s weakened tissues.

Mechanical load – the force transmitted through a joint during activity – is a major driver of joint degeneration. Importantly, not all load is harmful – regular moderate loading is beneficial for cartilage health. Routine movements and weight-bearing exercise help pump nourishing synovial fluid through cartilage and keep the tissue resilient. Problems arise when loading is excessive, abnormal, or applied without sufficient recovery. High-impact or heavy forces beyond what the cartilage can tolerate cause microdamage. For instance, an abrupt twist or hard landing might tear cartilage fibers or bruise the underlying bone, initiating a degenerative process. Even without a single injury, repetitive overloading accumulates wear over time. Years of manual labor or high-intensity sports – especially with poor technique or inadequate rest – can gradually erode cartilage as countless tiny stresses add up. Conversely, too little load can also be detrimental. Cartilage that isn’t used regularly can thin and weaken from disuse. The healthiest joints experience a Goldilocks balance of loading: enough stress to keep cartilage nourished, but not so much that it overwhelms the tissue’s structural integrity. When load repeatedly exceeds what cartilage can handle, the collagen framework breaks down faster than it can rebuild. This often triggers a biological cascade as well – overloaded cartilage and bone release inflammatory enzymes that further degrade the matrix. In this way, excessive mechanical stress and tissue degeneration reinforce each other, accelerating joint damage.

How we move is as important as how much we move. Joints are designed to work through a certain range of motion, and using that full range in varied ways helps protect against uneven wear. Repetitive movement in one plane or a very limited range can concentrate stress on the same cartilage area over and over. Over years, that area may wear down like a tire developing a bald spot. By contrast, moving a joint through its complete range and in different directions distributes forces more evenly across the cartilage surface. Greater movement variability also promotes better joint lubrication: when a joint is regularly taken through its full span, synovial fluid circulates to all areas of the cartilage. If part of the range is never used, that portion of cartilage might not get adequate nutrient-rich fluid. People who vary their physical activities and postures tend to have healthier joints than those with very repetitive routines. Our joints thrive on regular use – but not on exactly the same use all the time. Varying one’s movements throughout the day (and maintaining flexibility and muscle balance around the joint) helps prevent any single area from being overstressed. In sum, maintaining range of motion and diversity of movement are key to balancing out wear and tear.

“Time under tension” refers to how long a joint endures load continuously and how frequently those loads occur over time. The duration of loading makes a significant difference in cartilage health. Under normal conditions like walking, each load on the joint is brief and followed by relief, allowing cartilage to rebound and rehydrate. Cartilage can withstand these short, cyclic loads quite well. In contrast, prolonged static loading can be detrimental. If you hold a heavy posture or remain in one position for a long time (for example, hours of kneeling or carrying something without a break), the constant compression squeezes fluid out of the cartilage faster than it can be replenished. After an extended period of continuous pressure, the cartilage becomes dehydrated and thinner, and its cells become stressed from lack of nutrients. Experiments show that holding cartilage under heavy compression for hours can kill cells and damage the tissue, whereas the same total load applied in shorter bursts with rest causes far less harm. This helps explain why joints often feel stiff or sore after one has been in the same position for too long: the cartilage has been compressed and starved of fluid until the load is removed. Over the long term (years and decades), cumulative time under tension is a critical factor in joint aging. A knee that has spent decades under heavier loads – due to obesity, occupational strain, or high-impact athletics – is more likely to wear out than one that has had a lighter or more varied load history. Cartilage has limited capacity to adapt to chronically increased load; it does not significantly thicken or strengthen like muscle or bone might. Instead, excessive sustained loading gradually wears it down. That is why moderation and rest are vital. Joints need regular movement to stay healthy, but they also need periodic breaks from continuous strain. In practical terms, a person who runs or jumps intensely every single day without rest may start to experience joint pain and degeneration, whereas someone who intersperses intense days with lighter activity or rest days gives their cartilage a chance to recover. Ultimately, it is the extremes – either almost no joint use at all, or relentless overuse without recovery – that most often lead to degeneration.

In practical terms, this means staying active with well-balanced, varied exercise, using good form, avoiding long periods of inactivity or static posture, maintaining a healthy weight, and rehabilitating any joint injuries or imbalances. By keeping our joints moving but not chronically overloading them, we give cartilage the best chance to remain healthy. Joint degeneration is not inevitable – with sensible use and care, we can preserve mobility and joint function well into older age.

Alentorn-Geli, E., Samuelsson, K., Musahl, V., Green, C. L., Bhandari, M., & Karlsson, J. (2017). The association of recreational and competitive running with hip and knee osteoarthritis: a systematic review and meta-analysis. Journal of Orthopaedic & Sports Physical Therapy, 47(6), 373–390.

Eckstein, F., Hudelmaier, M., & Putz, R. (2006). The effects of exercise on human articular cartilage. Journal of Anatomy, 208(4), 491–512.

Krakowski, P., Rejniak, A., Sobczyk, J., & Karpiński, R. (2024). Cartilage integrity: A review of mechanical and frictional properties and repair approaches in osteoarthritis. Healthcare, 12(16), 1648.

Li, Y., Wei, X., Zhou, J., & Wei, L. (2013). The age-related changes in cartilage and osteoarthritis. BioMed Research International, 2013, Article ID 916530.

Lucchinetti, E., Adams, C. S., Horton, W. E. Jr., & Torzilli, P. A. (2002). Cartilage viability after repetitive loading: a preliminary report. Osteoarthritis and Cartilage, 10(1), 71–81.

Wang, X., Perry, T. A., Arden, N., Chen, L., Parsons, C. M., Cooper, C., Gates, L., & Hunter, D. J. (2020). Occupational risk in knee osteoarthritis: a systematic review and meta-analysis of observational studies. Arthritis Care & Research, 72(9), 1213–1223.