Strengthening your Achilles tendon requires heavy, slow loading performed consistently over at least 12 weeks. Unlike muscles, which respond to training within days, tendons adapt gradually by building new collagen fibers that increase thickness and stiffness. The good news is that the exercises themselves are simple. The challenge is doing them correctly, at the right intensity, and with enough patience to let the biology work.
Why Tendons Need Heavy Load to Adapt
When you load your Achilles tendon with enough force, pressure-sensitive receptors on the tendon cells open and allow calcium to flow in. That calcium triggers a signaling chain that tells the cells to produce more type I collagen, the primary structural protein in tendons. Over time, this leads to tendon hypertrophy: the tendon gets thicker and stiffer, which means it can handle greater forces before being damaged.
The key word is “enough.” Research has identified a clear intensity threshold: loads need to reach at least 70% of your one-rep max to reliably trigger these structural changes. Lighter loads might strengthen the surrounding muscles, but they won’t produce meaningful tendon adaptation. This holds true regardless of whether you’re doing slow lifts, quick reps, or eccentric-only work.
The Best Exercises for Achilles Strength
Heavy Slow Resistance Calf Raises
Heavy slow resistance (HSR) training is the gold standard for building tendon capacity. The concept is straightforward: perform calf raises with added weight, using a slow tempo of about 6 to 8 seconds per repetition (3 seconds up, 3 seconds down, or 4 and 4). You can do these on a leg press machine, a Smith machine, or standing on a step while holding dumbbells.
Start with a weight that challenges you for 3 to 4 sets of 6 to 8 repetitions at that slow tempo. One important detail: research shows that slower tempos reduce the actual load you can lift, and at around six repetitions with a 6-second tempo, you risk dropping below that 70% intensity threshold. So if you’re using a very slow tempo, keep the rep count moderate and the weight genuinely challenging. You should feel significant effort by the last two reps of each set.
Eccentric Heel Drops
The Alfredson protocol is the most widely studied eccentric program for the Achilles. You stand on the edge of a step, rise up on both feet, then slowly lower on one foot so your heel drops below the step level. The original protocol calls for 3 sets of 15 repetitions, twice daily, seven days a week for 12 weeks. That’s 180 reps per day.
While this program has helped many people, more recent reviews have questioned whether that aggressive daily volume is truly necessary or even optimal for everyone. The simplistic one-size-fits-all dosage has been challenged, with researchers noting a lack of evidence comparing different loading programs head to head. If you’re using eccentric heel drops as your primary approach, starting with the full protocol is reasonable, but adjusting volume based on how your tendon responds the next day is smarter than blindly following the numbers.
Isometric Holds
Isometric calf raises, where you hold a raised position without moving, can be a useful entry point if your Achilles is currently painful. Studies on Achilles tendinopathy have tested 45-second holds of the plantar flexors, with some participants reporting about a 1-point reduction in pain on a 10-point scale. Results are inconsistent: some people feel immediate relief, while others experience a temporary increase in pain. Isometrics are best used as a warm-up or pain management tool rather than a standalone strengthening strategy, since they don’t provide the through-range loading that drives the most robust collagen remodeling.
How Often to Train
This is where tendon biology diverges sharply from muscle training logic. After a heavy loading session, your Achilles tendon actually experiences a net decrease in collagen for the first 24 to 36 hours. Collagen synthesis then ramps up and peaks between 36 and 78 hours after exercise. In practical terms, the tendon needs up to 3 full days to recover and rebuild from heavy loading.
That means 2 to 3 heavy Achilles sessions per week, with recovery days in between, is likely more effective than daily training for building tendon strength. Training the tendon hard every single day doesn’t give it time to complete the repair cycle. On off days, normal walking and light activity are fine and even beneficial, just avoid high-intensity loading like sprinting, jumping, or heavy calf work.
How Long Adaptation Takes
Expect a minimum of 12 weeks of consistent training before meaningful structural changes occur in the tendon. In healthy subjects, 12 weeks of resistance training produces measurable tendon hypertrophy regardless of whether the exercises are concentric or eccentric. Full recovery from tendinopathy typically takes 6 to 12 months, with some intermittent discomfort considered a normal part of the process.
Tendons are remarkably resilient to losing size. Cross-sectional area only decreases during extremely prolonged periods of inactivity, so brief interruptions in your training won’t erase progress. But the flip side is also true: gains accumulate slowly and require sustained consistency. Think of tendon training less like a 6-week sprint and more like a season-long investment.
Monitoring Your Response to Load
The most practical way to gauge whether your loading is appropriate is to check how your Achilles feels the morning after a session. Some discomfort during exercise is acceptable, particularly if you’re working through tendinopathy. But if pain is noticeably worse 24 hours later or lingers into the second day, you’ve likely exceeded what the tendon can currently tolerate.
A progressive loading approach works best: increase exercise intensity based on your pain tolerance and functional capacity. If you tolerate a session well with minimal next-day soreness, nudge the weight up slightly the following week. If you’re flaring up, hold steady or reduce load. Complete rest is not recommended, even for painful tendons. Maintaining some level of loading, even at reduced intensity, keeps the collagen turnover cycle active.
Practical Modifications
If your Achilles is irritable, performing exercises with a heel lift or wedge under your heel can reduce strain on the tendon. Heel lifts decrease the amount of dorsiflexion (the motion of your shin tilting forward over your foot), which lowers both the stretch and compressive forces on the Achilles. A 20-millimeter lift, roughly the thickness of three stacked coins, has shown the most consistent benefit in studies on insertional Achilles tendinopathy.
You can also apply this principle through footwear. Shoes with a higher heel-to-toe drop (10 to 12mm) place less strain on the Achilles during daily activities compared to flat or minimalist shoes. If you’re in the early stages of building tendon tolerance, this simple change can reduce cumulative irritation throughout the day and let you get more out of your dedicated strengthening sessions.
Putting a Program Together
A practical weekly plan might look like this: two to three sessions of heavy slow calf raises, spaced at least two days apart. Each session includes 3 to 4 sets of 6 to 8 reps at a slow tempo with at least 70% of the maximum weight you can lift for one rep. If you’re dealing with tendon pain, start each session with a 45-second isometric calf hold to settle symptoms, and use a heel wedge if needed.
Progress by adding small increments of weight every one to two weeks. After 12 weeks, reassess. Your tendon won’t feel dramatically different day to day, but you should notice that activities that previously caused stiffness or soreness, like running, hiking, or climbing stairs, feel easier and produce less reaction afterward. That reduced sensitivity is the tendon telling you it’s structurally stronger.