Blog 1: Muscle Contractions
Part 1: The Foundation Every Athlete Needs to KnowDr. Keirstyn
Welcome to Understanding Muscle Contractions! In this 5 part blog series, Dr. Keirstyn of Endurance Therapeutics walks us through one of the most fundamental concepts in human performance and makes it actually useful for your training, your injury prevention, and your longevity in sport. Whether you are a triathlete, a hockey player, a runner, or just someone who wants to move well and stay healthy, this series is for you.
We are starting with the foundation: what a muscle contraction actually is, why there are different types, and why understanding the difference matters more than most athletes realize.
What Actually Happens When a Muscle Contracts?
Most people think of a muscle contraction as simply a muscle getting shorter. That is one version of it. But a muscle can also produce force while staying the same length, or even while getting longer. These three scenarios are the backbone of this series and they are not just anatomy trivia, they determine how you train, how you get injured, and how you recover.
At the most basic level, a muscle contraction happens when the nervous system sends a signal to muscle fibres telling them to generate tension. The actin and myosin filaments inside the muscle fibre slide together, creating force. What happens to the muscle as a whole, whether it shortens, holds, or lengthens, depends on the relationship between the force the muscle is producing and the external load it is working against.
Think of it this way. If you pick up a coffee cup, your bicep shortens to lift it. If you hold the cup still with your arm bent, your bicep maintains tension without changing length. If someone slowly pushes your arm down while you resist, your bicep is generating force while it gets longer. Three different scenarios, same muscle, completely different demands on the tissue.
Why Do the Different Types Matter?
Each type of contraction trains the muscle differently, stresses the tissue differently, and has different implications for performance and injury risk. This is not a small distinction. Research consistently shows that different contraction types produce different adaptations in strength, power, and tissue resilience — and that training only one type leaves significant gaps.
Here is why this matters in practice:
Most gym exercises combine multiple contraction types in a single movement: a squat involves all three within one repetition
Most sport-related injuries happen during one specific type of contraction, and knowing which one tells you a great deal about prevention
Rehabilitation protocols are built around contraction type, the order in which they are introduced is not arbitrary, it is based on the mechanical stress each type places on healing tissue
Training programmes that emphasize only one contraction type develop imbalances that accumulate over a season
A Quick Overview of the Three Types
Before we go deep on each one in the posts that follow, here is the landscape:
Isometric Contractions:
Where the muscle produces force without changing length. The joint does not move. This is the contraction of stability, of holding position, of the quiet work that holds everything together under load. We are starting here in Part 2 because it is the most underappreciated of the three and arguably the most important for injury prevention.
Concentric Contractions:
Where the muscle shortens as it produces force. This is the contraction most people picture when they think of strength training. The bicep curling a weight up. The quad driving you out of a squat. It is the power-production phase of most movements and the type of training most athletes already do plenty of.
Eccentric Contractions:
Where the muscle lengthens while still under tension. This is the braking phase. The controlled lowering of a weight. The quad absorbing landing force. Eccentric contractions produce the most force, create the most muscle damage, drive the most adaptation, and are responsible for the largest proportion of sports injuries. They also have the most robust evidence base for rehabilitation of tendon injuries. We will spend significant time on this one in Part 4.
How This Applies to You Right Now
Regardless of your sport, your training almost certainly has an imbalance somewhere across these three types. Most recreational athletes overtrain concentric movements and undertrain eccentric and isometric ones. This creates a body that is good at producing force but not at controlling it. Which is exactly the environment where injuries happen.
Over the next four parts we are going to break each contraction type down in detail, look at where it shows up in sport and training, and give you the understanding to make smarter choices about how you train and how you protect yourself.
Up Next: Isometric Contractions
Part 2 opens with isometric contractions, the unsung hero of athletic performance. You are holding positions all day in training and in sport without realizing it, and the strength of those holds is one of the strongest predictors of injury resilience we have. See you there.
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Understanding how your muscles work is the first step to training smarter and staying healthier. If you want to dig into what this means specifically for your body and your sport, reach out to book an assessment at Endurance Therapeutics.
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