Stiff Ankles, Weak Kick? Flexibility and the Adult-Onset Swimmer

Watch an adult-onset triathlete kick with a board and you will often see a familiar pattern: the feet hang at an angle, the knees bend a lot, and the swimmer moves slowly or not at all. Runners and cyclists in particular tend to have ankles that don't point well. Former swimmers, by contrast, can often lay their feet almost flat.

Stiff ankles are a common explanation for a weak kick, and ankle stretches are a common prescription. This article looks at how strong the link is, whether stretching changes it, and how much the kick matters in a triathlon swim anyway.

The evidence here is thin. Almost all of it is in competitive swimmers, several of the key studies are small, and none involves adult-onset swimmers or triathletes. That gap is flagged throughout.

Neighbouring TriForward articles cover related ground. "Kick, Pull Buoy, Paddles" looks at kickboards and other tools, "Six Months, Same Pace" covers why age-group swimmers plateau, and "Swimmer's Shoulder in Triathletes" covers the shoulder. This article stays on the ankle, with a short note on the shoulder at the end.

Why ankles matter in the kick

In the flutter kick, the foot acts a bit like a flexible fin. When the toes point (plantar flexion), the top of the foot faces backwards during the downbeat and can push water behind you. When the ankle can't point, the foot sits closer to a right angle to the leg. On the downbeat, more of the sole faces down or even forwards, which pushes water down rather than back and can add drag.

That is the mechanical logic. Runners and cyclists may have less plantar flexion range because their sports rarely take the ankle to full point, and because years of loading may stiffen the calf and the front of the ankle. That second part is plausible but hasn't been tested directly in triathletes.

The flutter kick correlation

A 2009 study by McCullough and colleagues in the Journal of Strength and Conditioning Research tested 20 women: 10 NCAA Division I collegiate swimmers and 10 recreational swimmers, with a mean age of about 21. They measured ankle flexibility, body size, leg length and vertical jump, and timed a 50 m front crawl and a 22.86 m (25-yard) flutter kick.

• Ankle plantar flexion correlated with flutter kick speed (r = 0.509), a moderate relationship.
• Kick time and 50 m swim time were strongly related (r = 0.790).
• Body size, leg length and vertical jump didn't predict kick or swim speed.

The authors concluded that ankle flexibility appears to influence flutter kick ability and recommended that swimmers develop it.

This was a small, all-female, cross-sectional study. The more flexible swimmers were likely to be the more experienced ones, so ankle range may simply mark years of swimming rather than cause faster kicking.

Taping the ankles: a test of cause

A 2022 study by Kuhn and Legerlotz in Frontiers in Sports and Active Living went a step further by changing ankle range and measuring the result. They tested 10 well-trained swimmers (5 men and 5 women), aged about 22, with around 16 years of training.

Each swimmer did underwater dolphin kicking, at a fixed kick rate, under three conditions:

• Restricted: elastic tape on both feet reduced maximum plantar flexion by about 10%.
• Normal: no intervention.
• Increased: passive-dynamic stretching just before testing increased maximum plantar flexion by about 7%.

The results:

• Restricted: 1.13 metres per second.
• Normal: 1.20 metres per second.
• Increased: 1.22 metres per second.

Restricting the ankle significantly reduced speed and kick efficiency compared with both other conditions. But the stretched condition wasn't significantly faster than normal. Kick frequency didn't change.

Inference: the restricted condition was about 6% slower than normal. Reducing ankle range clearly hurt; adding range acutely didn't clearly help. Ten swimmers is a very small sample, the kick was underwater dolphin kick rather than front crawl flutter kick, and only acute effects were measured. The authors themselves said long-term flexibility gains might act differently.

Strength may matter as much as range

A 2014 study by Willems and colleagues in Human Movement Science tested 26 competitive swimmers (the sex split wasn't given in the material checked). They measured ankle range and ankle strength, then timed maximal dolphin kicking.

• Dorsiflexor and internal rotator strength correlated with kick velocity.
• Active and passive plantar flexion range didn't correlate significantly with velocity.
• Taping to restrict plantar flexion and internal rotation did reduce velocity, and shifted the knee towards more bending.

The authors suggested that ankle strength exercises may improve dolphin kick, and that swimmers with restricted flexibility may benefit from a flexibility programme.

Inference: across competitive swimmers who all have reasonable range, strength appears to separate fast and slow kickers better than flexibility. Severe restriction, as in the taping conditions, does slow swimmers. A stiff-ankled adult-onset swimmer may sit closer to the taped condition than to the competitive swimmers' normal range, but that hasn't been measured.

How much does the kick add to front crawl?

This is the question that matters most for a triathlete. A 2017 study by Silveira and colleagues in the International Journal of Sports Physiology and Performance tested 29 masters swimmers (21 men and 8 women). They swam front crawl with and without the legs at six self-selected speeds, from very slow to maximal.

• The leg kick's contribution to speed rose with pace, from about -1% at the slowest speeds to about 11% at the fastest.

A negative value means that at very slow speeds, kicking contributed nothing to speed, or slightly less than nothing.

A 2014 study by Gourgoulis and colleagues in the Journal of Sports Sciences looked at sprinting. Nine female swimmers did maximal 25 m trials with and without a kick. Kicking increased speed and reduced trunk inclination by 13%, meaning the body lay flatter in the water. The authors suggested the kick helps both by adding propulsion directly and by reducing the body's angle, which cuts drag. Arm propulsion itself didn't change.

Inference: at steady triathlon pace, the kick's direct propulsion is likely to be small. Its more important role may be keeping the legs high and the body flat. That changes the goal for a stiff-ankled triathlete: a kick that doesn't drag the legs down matters more than a kick that drives you forward.

Can you change ankle range?

Range at the ankle is trainable, but less so than at some other joints. In a 2024 meta-analysis of 77 studies with 3,870 participants, Konrad and colleagues found that regular stretching produced a moderate overall increase in range of motion. Gains at the calf (triceps surae) were smaller than at the hamstrings or hip flexors, with an effect size of about 0.7 compared with about 1.2 and 1.1. The authors suggested the ankle's smaller total range may explain part of this.

Most calf-stretching trials measure dorsiflexion, pulling the toes up, which is what runners need. Pointing the foot in the water relies on plantar flexion range, which is limited by the muscles and tissues at the front of the ankle. Inference: an ordinary runner's calf stretch probably doesn't target the range a swimmer needs. No trial has tested a plantar flexion stretching programme in adult swimmers.

What about wetsuits and pull buoys?

In most triathlons, you race in a wetsuit, which adds buoyancy, particularly to the legs. Inference: if the kick's main job at triathlon pace is to keep the legs up, a wetsuit does some of that job for you, which may reduce how much a stiff ankle costs on race day. It doesn't help in non-wetsuit races, in the pool or in warm-water events. TriForward's "Kick, Pull Buoy, Paddles" covers why relying on a pull buoy in training can hide a body-position problem rather than solve it.

Who these studies tested

Every study above was in people who already swim well. The McCullough study compared collegiate swimmers with recreational swimmers, all young women. The Kuhn and Willems studies tested trained and competitive swimmers with many years in the water. The Silveira study is the closest to triathletes: masters swimmers, mostly men, swimming across a range of speeds. The Gourgoulis study was nine women sprinting.

None tested adult-onset swimmers, and none tested triathletes. That matters because:

• Range may differ a lot. A runner who has never pointed their feet may sit far outside the range of the competitive swimmers studied.
• Skill differs. Experienced swimmers can use the range they have. A beginner may not, however flexible they become.
• Pace differs. Most triathletes swim at steady speeds, where the Silveira data suggest the kick adds least.

Inference: the findings give a reasonable starting point, but the size of the effect for a stiff-ankled triathlete is unknown. It could be larger, because their range is more limited, or smaller, because body position and arm technique limit them first.

Practical options

The following is TriForward's inference from the evidence above, not a tested programme.

1. Fix body position first. Head down, eyes towards the bottom, and a small, quick kick from the hip. A big knee-driven kick with stiff ankles can increase drag.
2. Keep the kick small and relaxed. Many adult swimmers kick hard and slow down. A gentle two-beat or relaxed six-beat kick may cost less energy.
3. Try short kick sets with fins. Fins hold the foot in a more pointed position and let you feel the movement. Use them in short blocks so the calves and arches can adapt.
4. Add gentle plantar flexion stretching if you want to experiment. Seated, with the leg straight, point the foot and gently press the top of the foot towards the floor; hold 30 to 60 seconds, most days, for several weeks. Avoid forcing the position.
5. Add ankle strength work. Resisted dorsiflexion and plantar flexion with a band, and calf raises, are low-risk and may help more than range alone, given the Willems findings.
6. Retest. Time a short kick set or film your kick every six to eight weeks.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 44-year-old runner has started swimming for her first sprint triathlon. With a kickboard she barely moves, and her coach notes that her feet hang at an angle and her legs sink.

Based on the evidence above, she might:

• Work on body position first, since a flat body probably matters more at her pace than kick propulsion.
• Use a relaxed, small kick in full stroke rather than trying to kick hard.
• Try short fin sets to learn the feel of a pointed foot.
• Add ankle stretching and band work at home, treating it as an experiment rather than the main fix.
• Accept that her kick may stay weak, and that in a wetsuit it may matter little to her race time.

A note on shoulders

The same logic is often applied to the shoulders: runners and cyclists with stiff shoulders may struggle with a high-elbow catch or a relaxed recovery. The evidence for flexibility training improving the catch in adult swimmers is no stronger than for the ankle. For shoulder health, TriForward's "Swimmer's Shoulder in Triathletes" argues that load, not just technique, drives pain, and "Dryland Strength That Transfers to the Water" covers what strength work helps.

Common mistakes

• Kicking harder to fix a weak kick. With stiff ankles, more effort often means more drag.
• Spending a large share of swim time kicking. At triathlon pace, the kick adds little speed.
• Forcing ankle range. Sitting back on pointed feet can stress the knees, and forced stretching can strain the front of the ankle.
• Expecting stretching to change speed quickly. In the one trial that tested it acutely, it didn't.
• Ignoring strength. In competitive swimmers, ankle strength predicted kick speed better than range.

What we don't know

• Whether ankle flexibility training improves kick or swim speed in adult-onset swimmers or triathletes. No trial has tested it.
• Whether runners and cyclists actually have less plantar flexion range than other adults. It's widely assumed but hasn't been tested here.
• How much a stiff ankle costs in a wetsuit at race pace.
• Whether findings from dolphin kick transfer to the flutter kick in front crawl.

References

• McCullough AS, Kraemer WJ, Volek JS, Solomon-Hill GF, Hatfield DL, Vingren JL, et al. Factors affecting flutter kicking speed in women who are competitive and recreational swimmers. Journal of Strength and Conditioning Research, 2009;23(7):2130–2136. doi:10.1519/JSC.0b013e31819ab977
• Kuhn J, Legerlotz K. Ankle joint flexibility affects undulatory underwater swimming speed. Frontiers in Sports and Active Living, 2022;4:948034. doi:10.3389/fspor.2022.948034
• Willems TM, Cornelis J, De Deurwaerder L, Roelandt F, De Mits S. The effect of ankle muscle strength and flexibility on dolphin kick performance in competitive swimmers. Human Movement Science, 2014;36:167–176. doi:10.1016/j.humov.2014.05.004
• Silveira RP, de Souza Castro FA, Figueiredo P, Vilas-Boas JP, Zamparo P. The effects of leg kick on swimming speed and arm-stroke efficiency in the front crawl. International Journal of Sports Physiology and Performance, 2017;12(6):728–735. doi:10.1123/ijspp.2016-0232
• Gourgoulis V, Boli A, Aggeloussis N, Toubekis A, Antoniou P, Kasimatis P, et al. The effect of leg kick on sprint front crawl swimming. Journal of Sports Sciences, 2014;32(3):278–289. doi:10.1080/02640414.2013.823224
• Konrad A, Alizadeh S, Daneshjoo A, Hadjizadeh Anvar S, Graham A, Zahiri A, et al. Chronic effects of stretching on range of motion with consideration of potential moderating variables: a systematic review with meta-analysis. Journal of Sport and Health Science, 2024;13(2):186–194. doi:10.1016/j.jshs.2023.06.002