Your Achilles And Calves
Trail Notes | Tendon Health + Durability
for the lower leg that carries you further
Your Achilles
And Calves.
Tendons do not respond to rest. They respond to load, recovery, and the patience to build one before asking too much of the other.
Your Achilles and calves are doing a lot of work right now. Every climb, every descent, every long hour on your feet. They are your connection between the engine above and the ground below, and when they start grumbling, it is worth paying attention before it becomes something bigger.
This Trail Note is not a red-flag warning. It is a practical guide to keeping your lower leg strong and resilient across a training block: what to actually do, how to read the signals, and when to ease off versus push through.
As female trail and ultra athletes, we also carry a few extra layers here that are worth understanding, including how hormones intersect with tendon health. So let us get into it.
The goal is not to be careful. The goal is to be strong enough that careful is rarely needed.
Load the tendon progressively, adapt your technique on the hills, and fuel the tissue well. That is your best insurance.
Trail Note · 01
Tendons need load, not rest
This is the most important thing to know about Achilles management: passive rest does not fix tendons. It just gives them a temporary break before the same load returns and the same problem reappears.
What tendons respond to is progressive, manageable load. This is what stimulates collagen remodelling, builds the tendon-muscle unit's capacity to store and release energy, and creates the resilience that allows you to train through a big block without breaking down.
The clinical approach that has the most support is called Heavy Slow Resistance training: loading the calf-Achilles complex with enough weight that the tissue has to work, at a pace slow enough that it cannot rely on momentum. It sounds simple, and it is. The trick is doing it consistently.
Load it thoughtfully. You are not protecting it by avoiding it.
Trail Note · 02
The two exercises that actually build tendon strength
Two to three times a week is enough if you do them properly. Both exercises target different parts of the calf complex, which is why you need both: single-leg calf raises (gastrocnemius) and seated soleus raises (soleus, the deeper muscle that takes a high share of load during trail running).
Single-leg calf raise
Stand on a step. Lower your heel slowly over 3 seconds, then raise back up over 3 seconds.
Load it: hold a weight or use a heavy backpack. The last few reps should be genuinely difficult.
3 sets of 10 to 15 reps. If it feels easy, add more load.
Seated soleus raise
Sit with your knees bent at 90 degrees, feet flat. Place a weight on your thighs. Raise your heels slowly over 3 seconds, lower over 3 seconds.
The bent-knee position isolates the soleus, which works hard on every climb and during long hours of hiking.
3 sets of 10 to 15 reps.
You do not need to do these on your hardest training days. Three sessions a week, treated seriously, is your best long-term insurance policy.
Trail Note · 03
Hill technique: going up
Uphill running increases the tensile load on the Achilles significantly. The tendon is working near its lengthened position under load, which is why steep climbing can trigger mid-Achilles flare-ups in some of us.
Two cues that make a real difference on the climbs:
Let your heel drop
Rather than staying high on your toes, allow your heel to drop into the ground (especially when power-hiking). This shortens the working range and reduces sustained tension on the Achilles through the climb.
Stay tall, not bouncy
Keep a relatively upright posture rather than bouncing up onto your forefoot with each step. Efficient uphill hiking looks steady and grounded, not springy. Save the spring for later in the race.
Trail Note · 04
Hill technique: coming down
Downhill running produces high peak ground reaction forces, placing a heavy eccentric braking demand on your calves and soleus. This is often where calf strains happen, and where an irritated Achilles gets significantly worse if the technique is off.
Land midfoot with a slight forward lean
Landing with a slight forward lean reduces heavy heel braking through the calves. Think of absorbing the impact softly rather than stopping yourself with each foot strike.
Control, not braking
The calves do significant work on descent regardless. Your job is to reduce the unnecessary load. Fast turnover and shorter steps let you stay in control without hammering the lower leg on every contact.
Trail Note · 05
Layer your vertical gain gradually
Tendons adapt more slowly than muscles. You might feel strong enough to push vertical gain week after week, but the tissue is working on a longer timeline than your legs are telling you.
After a big climbing week, treat the following week as easier on the hills. This is not backing off. It is periodization applied to vert, the same principle we use for overall load: build, consolidate, build again.
The rule to hold onto: do not stack a jump in speed and a jump in climbing in the same week. If you are adding vert, keep pace honest. If you are pushing pace, keep the hills manageable.
Her Trails coaching cue
One variable at a time. Vert adaptation follows the same rules as the rest of your block: build the stimulus, then give it time to land.
Trail Note · 06
Footwear and support
If your Achilles is grumbling or you have a heavy vert week ahead, your footwear choice matters more than usual.
Heel drop
A higher heel-drop shoe (8mm or more) takes tension off the tendon by shortening the calf's working range. On big vert weeks or during a flare-up, this is a simple mechanical fix.
Heel lifts
A temporary 3 to 5mm heel lift inside your shoe achieves the same effect and works well if you want to stay in your usual shoe. Useful during an acute period rather than as a permanent solution.
Calf sleeves
Medical-grade calf sleeves reduce lower-leg muscle vibration and support circulation on long days. Particularly useful during long humid ultras where legs take a beating over many hours on feet.
Race day
Do not debut new footwear on race day. If you want to trial a different shoe or a heel lift during a flare-up, test it in training first so you know how your body responds.
Trail Note · 07
Fuel the tendon (it matters more than you think)
Tendon repair is a nutrition-dependent process. The collagen matrix that makes up your Achilles is built from protein, and without adequate building blocks, the remodelling process slows down regardless of how well you load the tissue.
Do not undereat in the bigger weeks. Skimping on carbohydrates increases your risk of RED-S (Relative Energy Deficiency in Sport), which in turn affects tendon health and collagen synthesis. The tendon needs energy to recover, not just protein.
What to prioritise
Adequate total protein across the day, spread across meals rather than loaded into one.
Collagen-containing foods or a collagen supplement (10 to 15g alongside vitamin C) taken 30 to 60 minutes before your strength session or long run. The vitamin C supports synthesis.
Enough carbohydrates in your bigger training weeks so your body has the energy to repair and adapt, not just survive the sessions.
Her Trails coaching cue
Underfuelling is a tendon risk. If you are in a heavy block and the Achilles is grumbling, check your food first before you assume it is a training load problem.
Trail Note · 08
The female factor: hormones and tendon health
As female trail athletes, tendon health is not purely mechanical. Estrogen receptors are present on tenocytes (the cells that build and repair tendon tissue), and fluctuations in estrogen appear to influence collagen synthesis and tendon behaviour. The research is still developing, and the picture is mixed, but here is what is worth knowing for training.
Lower estrogen states (including around menstruation, in perimenopause and menopause, and in those experiencing RED-S) have been associated in some studies with reduced collagen production and changes in tendon tissue quality. This does not mean your tendons are fragile in these phases. It means load management, fuelling, and strength training matter even more during them.
You do not need to modify your entire program around your cycle or hormonal phase. But if you notice your Achilles is more reactive at predictable times in your cycle, that pattern is worth tracking and worth mentioning to your physio.
Awareness is not alarm. Your hormones are a variable worth knowing, not a reason to fear the training.
Trail Note · 09
Your pain guide: what is normal and what is not
Tendons can be loaded even when they are not completely comfortable. The line between productive discomfort and a warning sign is something worth understanding clearly, so you are not second-guessing every niggle.
More likely to be fine
Discomfort during loading that sits below 3 to 4 out of 10 on your pain scale.
Some morning stiffness in the first few steps that loosens up quickly once you are moving.
Mild tightness during the first kilometre of a run that settles once you are warmed up.
Worth paying attention to
Pain that climbs above 4 out of 10 during the session and does not settle back down.
Discomfort that changes how you are running: shortened stride, altered gait, compensating in the hip or knee.
Swelling, visible thickening, or tenderness when you press directly on the tendon.
Pain near the heel bone (insertional) rather than mid-tendon. These respond differently to load and need a physio's eye.
Trail Note · 10
The 24-hour rule
This is the simplest and most reliable feedback loop you have. After a run or strength session, how does the tendon feel the next morning?
If it has settled back to baseline within 24 hours, the session was appropriate. Continue. If it is still grumbling the next day, that is your cue to dial back the run volume and keep your time on feet with something lower-impact (bike, swim, walk), rather than pushing through and compounding the load.
You do not need to stop. You need to be smart about what replaces the session temporarily.
Still niggly tomorrow? Dial it back today. Not all the way off. Just enough to let it settle.
Trail Note · 11
Early warning signs: catch them before they become something bigger
The athletes who stay in training longest are not the ones who never get niggles. They are the ones who pick up the signals early and respond before a minor irritation becomes a significant injury.
Two things that are worth noting and telling your physio: where exactly you feel the discomfort (mid-tendon versus down near the heel bone), and how long it has been present. These two pieces of information help determine whether you are dealing with acute or chronic tendinopathy, and the loading approach differs significantly between them.
Flag these to your physio sooner rather than later
Morning stiffness that hangs around longer than a few minutes and does not fully clear.
Any pain that changes the way you are running, even subtly.
A niggle that has been present for more than two weeks without improving.
Discomfort specifically near the heel bone (insertional Achilles) rather than the middle of the tendon.
Catch the niggles early and adjust before they become something bigger.
The physio who sees you at week two of a niggle can usually keep you training. The one who sees you at week eight often cannot.
Trail Note · 12
The lower leg you can rely on
Your Achilles and calves are not a problem to manage around. They are tissues that respond predictably to the right inputs: consistent load, good technique on the hills, footwear that supports the demands of the week, fuel that gives the body what it needs to rebuild, and the awareness to read the signals and respond early.
None of this requires a perfect block or a perfectly cooperative tendon. It requires being the kind of athlete who pays attention, adjusts before the signals get louder, and keeps making good decisions across the weeks.
That is what durable training looks like. And durable training is what gets you to the start line in the shape you worked for.
Strong tendons are built across weeks, not fixed in days.
Load them. Fuel them. Adapt technique on the hills. Respond early. Stay in the game.
build the lower leg that carries you further
Written by the Her Trails coaching team
Trail Notes are evidence-informed coaching journals written for women who train, race and run on trails. Made to be absorbed in ten minutes and remembered for a season.
Sources: Frizziero et al., 2014 (Muscles, Ligaments and Tendons Journal) and referenced primary studies. Evidence cited is preliminary or mixed; consult a physiotherapist or sports medicine professional for individual guidance.
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