Is Your Achilles Really “Tight” — or Just Under-Prepared?
If you’re a runner, a tight Achilles probably feels familiar.
The usual response? Stretch it.
But in clinical practice — and in the research — that “tight” feeling is rarely a flexibility problem. More often, it’s a signal that the tendon isn’t handling load as efficiently as it could.
Why Stretching Feels Good (But Doesn’t Fix the Problem)
Stretching can temporarily reduce the sensation of tightness, which is why it’s so appealing.
However, research consistently shows that stretching:
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Has minimal impact on tendon mechanical capacity
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Does not meaningfully improve how the Achilles handles running loads
So while stretching may make symptoms feel better in the short term, it doesn’t change the thing that matters most for runners: how efficiently the tendon stores and releases energy.
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Achilles Stiffness: A Performance Advantage
In tendons, stiffness isn’t a flaw — it’s a feature.
A stiffer Achilles tendon:
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Deforms less under load
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Experiences less strain with each step
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Transfers force more efficiently between muscle and ground
This has real performance implications. Muscles use the least energy when they stay relatively still. When paired with an appropriately stiff tendon, the soleus muscle can operate at ~15% higher efficiency (Böhn et al., 2021). More recently, increased Achilles stiffness has been associated with a lower metabolic cost of running, meaning you expend less energy to hold the same pace.
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What This Means for Running Performance
Heavy calf loading doesn’t just strengthen muscle — it changes the tendon itself.
In trained athletes:
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Achilles stiffness increases of ~20–40% have been observed
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One study showed a ~31% increase with structured heavy calf training
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This produced an average ~4% improvement in running economy
That improvement is on par with the performance gains seen with carbon-plated racing shoes.
A stiffer tendon also:
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Strains less with each step
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Creates less muscle damage
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Supports better recovery between training sessions
Which means more consistent training over weeks and months.
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Durability: Why Stiffness Matters Late in Runs and Races
Tendon stiffness decreases during long runs.
After a 90-minute run:
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Achilles stiffness can drop by ~9%
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Energy cost increases by ~11 joules per stride (Farris et al., 2018)
Over thousands of strides, this becomes significant.
Athletes with higher baseline stiffness experience:
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Smaller stiffness losses during long runs
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Lower increases in late-race energy cost
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Less eccentric calf muscle damage
Estimated marathon impact:
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Lower baseline stiffness: 4–10 minutes slower
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Higher baseline stiffness: 3–7 minutes slower
That difference often shows up in the final third of a race — when form starts to fall apart.
Age and the Achilles Tendon
As runners age:
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Tendons naturally lose stiffness
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Older athletes show greater stiffness loss after long races
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Late-race energy cost increases more dramatically
This makes intentional tendon loading increasingly important with age — not less.
Maintaining Achilles stiffness is linked to:
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Better performance
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Reduced injury risk
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Improved late-race durability
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Greater tolerance to training volume
Why Running Alone Isn’t Enough to Train the Tendon
Running loads the Achilles — but not in the way tendons need to adapt.
Key limitation:
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Ground contact time is very short (fractions of a second)
Tendons adapt best when:
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Strain is held in the ~4.5–6.5% range
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Load is sustained long enough to reach tendon cells
Research suggests:
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~300 milliseconds is required for strain to reach the cellular level
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Practically, 3–4 second holds provide meaningful adaptation time
This is why targeted strength work matters.
A Clinically Sound Achilles Loading Approach for Runners
Frequency: 2–3 sessions per week
Timeline: Meaningful changes in ~4–8 weeks (Tendon adaptation is slower than muscle — consistency matters)
Heavy Calf Raises
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3–4 sets of 6–10 reps per leg (enough load that you hit fatigue by 10 reps)
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Slow tempo with 3–4 second lowering
Isometric Calf Holds
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4 sets of 5 reps
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3-second hold, 1-second rest
Isometric Calf Pushes
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4 sets of 3 reps
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3-second push and hold
Progression:
Increase load every ~2 weeks, provided symptoms remain controlled.
Runner-Friendly Summary
If your Achilles feels tight:
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It’s usually not a flexibility problem
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Stretching may feel good but doesn’t improve tendon capacity
Why stiffness matters:
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Stiffer tendons are more energy-efficient
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Linked to better running economy and performance
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Helps protect against late-race fatigue
Why strength training is essential:
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Running alone doesn’t provide enough time under tension
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Tendons need sustained, heavy loading to adapt
What to do:
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Prioritize heavy and isometric calf loading
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Train the tendon 2–3x/week
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Expect meaningful changes in 4–8 weeks
Bottom line:
A well-prepared Achilles doesn’t feel “tight” — it feels reliable.
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The lower leg muscles and Achilles tendon. (Courtesy of The Journal of Musculoskeletal Medicine. © Steve Oh, CMI 2009.
WHAT IS A CONCUSSION?
LEARNING ABOUT WHAT A CONCUSSION IS AND THE RISK FACTORS ASSOCIATED WITH IT.
The best explanation I have heard to define a concussion is to describe it as an acceleration and deceleration injury to the brain. Instead of thinking of a concussion as simply a bruise on the brain, it’s now understood as damage to the brain's delicate nerve fibers (neurons), which can stretch and be disrupted under shearing and rotational forces. This triggers a chain reaction of changes that the nervous system works to fix.
The brain is maintained through the nervous system, both the sympathetic and parasympathetic nervous system help to guide physiology in the brain & providing it with the appropriate neurotransmitters and blood flow to function. Neurotransmitters are chemical messengers that help the brain communicate and function properly. When there is a disruption to these processes the brain and nervous system must work overtime to correct it on top of regular daily function. In addition to these changes, we see a diminished level of cerebral blood flow (blood flow into and within the brain) which means the brain receives less oxygen and fewer nutrients, which it needs to heal and function.
We are about to learn about the neurophysiology of the brain after a concussion – so buckle up!
Understanding of how ions operate within the brain have been heavily researched and demonstrated through the schematic below. Ions are tiny, charged particles, like calcium and potassium, that play a key role in how brain cells send signals and maintain balance. We can see that at the point of injury and for several hours, there are extreme changes that occur in the brain as a response to the neuronal changes, and while most of those ions return to their baseline, calcium ions stay high for 3-4 days, and cerebral blood flow operates at a lower threshold for up to 10 days.
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Think of brain cells as tightly controlled balloons. During a concussion, the structures controlling ion-flow become thinner, causing the cells to leak particles like potassium while taking in excess calcium, disrupting their balance. This causes a depletion of energy stores (ATP) and an increase of glutamate release. Glutamate is a chemical that helps brain cells communicate, but too much of it can cause an overload of calcium in the cells.
This overload damages the energy-producing parts of the cell (the mitochondria), making it even harder for the brain to recover. This means the brain is working extra hard to restore balance, but it doesn't have enough blood flow to supply the energy it needs.
For about 20% of people, concussion symptoms persist beyond 10-14 days, resulting in post-concussion syndrome (PCS). This means the brain takes more time to heal and symptoms can persist for weeks, months, or even years. The largest risk factors for not recovering from an acute concussion are:
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History of concussions
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Being female
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Having a high symptom load (multiple symptoms instead of just one or two)
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A history of anxiety or depression may slow recovery because the brain is already managing stress, making healing more difficult.
Once a patient enters PCS, the outcomes vary in time and level of return. Some patients if managed correctly can resume all their activities within 6 weeks, some take months or even years to recover.
New research by Chou T-Y et al. (2023), demonstrates longer lasting symptoms of a concussion can translate into higher rates of ankle sprains and ACL-injury. In this latest systematic review, of 27 studies with over 1500 participants, they compared concussion to non-concussion athletes, in their risk for lateral ankle sprain and ACL-injury. The study found that after a concussion, people often struggle with balance and slower movements, increasing their risk of injuries like ankle sprains or ACL tears. The time frame that this occurs ranges from 2-days to 34-months for an ankle sprain and 60 days following sport resumption to 6.5 years for an ACL-injury.
Remember, during concussion recovery, the brain works harder but has less blood flow, making it harder to perform even simple tasks. For example, when you look at an image on your phone or computer, your brain must process all the details like colors, shapes, and shadows to make sense of it. For a healthy brain, this is automatic. But for a concussed brain, it’s like trying to solve a puzzle while someone is shouting questions at you, and the lights flickering on and off—it quickly becomes overwhelming.
For these reasons, it’s crucial to seek guidance from a specialist in concussion rehabilitation after a concussion. You want to make sure that you have appropriate guidance through the first two weeks after the concussion to help prevent the occurrence of entering PCS.
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