Science: aging, ankle strength, and running barefoot

Blog entry posted by Jon from PDX, Apr 30, 2019.

Like running? Want to keep running well as you age? Consider running barefoot. Here's one of many possible arguments why:

Ankles, not knees or hips, are the joints that are primarily responsible for age-related declines in running performance.^1 Barefoot running requires more effort from -- and therefore generates more strength in -- the ankle.^2 Consequently, running barefoot will help you increase or maintain ankle strength as you age, keeping this creeping chronological anchor at bay.

Let's look more closely at the research.

Kulmala et al wrote "Which muscles compromise human locomotor performance with age?", published in the Journal of The Royal Society Interface.^1 This study tested 39 healthy male athletes in three different age groups (~26, ~61, and ~78 years) and found, among other things, both significant and substantial differences in motion and power of ankles as well as hips between its age groups.

For example, the youngest group had 25% more ankle plantar flexion (where the sole of the foot flips down, as when landing on the forefoot or pushing off for the next step) (p<0.001), 31% more ankle joint power absorption (p<0.05), and 41% more power generation (p<0.001) than the oldest athletes. Meanwhile, the oldest athletes showed more hip flexion (p<0.01 than the youngest and p<0.05 than the middle group) and hip extensor power (41% more than the youngest, p<0.05).

Kulmala et al propose that, because the majority of ankle power is generated from the series of elastic structures -- tendons and ligaments -- between the calf muscles and the sole of the foot, "less efficient utilization of the stored elastic energy may be one key mechanism to explain impaired ankle propulsion among older adults during locomotion."^3

So, as we age, our ankles grow weaker, partly due to a decline in muscle power but also partly due to a decline in the ability of our elastic bits to hold and transmit tension. Can we exercise those muscles and tendons to maintain or restore that lost power? Yes, yes we can.

Holzer et al wrote "The role of muscle strength on tendon adaptability in old age", published in the European Journal of Applied Physiology.^4 This study tested 30 women with healthy lower limbs (~65 years old) for ankle plantar flexion strength and the size and properties of their Achilles tendons. While no causal relationships were sought, this study did find evidence to support the conclusion that stronger calf muscles, such as the medial gastrocnemius, were associated with improved elasticity of the Achilles tendon, "in line with most exercise intervention studies with older adults, where the magnitude of post-exercise adaptations in tendon stiffness and Young's modulus seem to be comparable to younger adults."

In other words, if you exercise your ankle plantar flexion muscles -- your Achilles tendons and the calf muscles which drive them -- you will be directly addressing the primary issue faced by older runners. But, can we do that while running? I mean, I know everybody loves going to the gym, but wouldn't it be better if this all happened automatically while running? Yes? Yes! In two words: go barefoot.

Sinclair et al wrote "Modeling of muscle force distributions during barefoot and shod running", published in the Journal of Human Kinetics.^2 This study tested 15 male runners (~28 years old) at a pace of 6:41/mile (4:09/km, 4 m/s) and found that, for a given athlete, running in shoes meant exhibiting more hip joint flexion and less ankle plantar flexion. (These runners showed hip peak flexion of 41.9 degrees while shod and 37.2 degrees while barefoot, and ankle relative range of motion of 9.2 degrees while shod and 19.6 degrees while unshod.) Moreover, the types of muscles uses varied significantly: while shod, runners emphasized their front-of-leg muscles (e.g., tibialis anterior at a peak force of 6.1 N/kg shod compared to 3.9 N/kg barefoot), and, while barefoot, runners emphasized their back-of-leg muscles (e.g., medial gastrocnemius at a peak force of 15.0 N/kg barefoot compared to 11.4 N/kg shod).

In other words, if you want your training to mimic the consequences of aging -- to have stronger hips and weaker ankle plantar flexion -- you should run with shoes. If, however, you want to train your body to be strong where aging is most likely to weaken you, then you should run barefoot.

To be clear: aging is still a fact of life and Western medicine is only beginning to study the nuances between different kinds of physical activity. Don't trust my interpretation of these articles over your doctor's advice or even over your own, hard-won wisdom. I don't advocate barefoot running as the one true cure-all. I do, however, find it to be enormously beneficial in my own life, and I wouldn't have tried it had not others presented their own viewpoints, so I merely offer my perspective for you to reject or accept on its own merits.

1: Kulmala, Juha-Pekka et al. Which muscles compromise human locomotor performance with age? J R Soc Interface. 2014 Nov 6.

2: Sinclair, Jonathan et al. Modeling of muscle force distributions during barefoot and shod running. J Hum Kinet. 2015 Sep 29.

3: I thank Kulmala et al for mostly writing about "running" rather than "rapid terrestrial locomotion" as seen elsewhere in the jargon of scientific journals.

4: Holzer, D. et al. The role of muscle strength on tendon adaptability in old age. Eur J Appl Physiol. 2018 Aug 7.
Jon from PDX

About the Author

Jon is a nerd with an affinity for sport. He loved playing soccer until a growth spurt led to knee pains that ended his running career, but went on to bike recreationally and row competitively while studying physiology and psychology (go, uh, Raiders?). He then studied law (go Irish!), and became a business writer (“Shark Tank” is for entrepreneurs on Easy Mode), and is currently running again for the first time in decades thanks to going barefoot.