The Wobbling Mass Effect: Forefoot Strike vs Heel Strike

Researchers have long known that the wobbling mass effect allows heel strike runners to manage impacts, preventing impacts from exceeding joint loading limits. However, fatigued state during running can trigger changes in the wobbling mass effect, resulting in joint forces that exceed tolerance and cause injury.

In running, the wobbling mass effect explains how muscle tuning as well as soft tissue movements dampen impact.

Wobbling Mass Effect
Heel strike running (left) may put the wobbling mass effect to a different and more complex use compared to forefoot running (right).

The Wobbling Mass Effect – Heel Strike vs Forefoot Strike

Previous studies showed that soft tissue movements are energetically expensive. Therefore, impact forces may shape energy demands whereby running styles that are forceful, such as heel strike running, may be more energetically taxing than running styles associated with less impact production such as forefoot running.

More recently, a study by Schmitt and Gunther (2011) looked for a link between the wobbling mass effect and net energy loss in heel strike running:

  • the net loss due to wobbling in heel strike running ranged from 30 to 60 J per stance phase.

Similar studies found a net joint energy release in all three leg joints during stance which compensated for the loss in energy due to wobbling. However, the current study found the wobbling mass loss was twice as high as leg dissipation and about half of the maximum energy stored in the leg.

Blickhan et al. also found that impacts are avoided  by deceleration which involves enormous energetic costs and control efforts. Because deceleration is high in heel strike running, the findings hint that heel strike running is possibly less efficient than forefoot running.

Less Wobbling in Forefoot Running

Looking at the evolutionary basis of human running, humans evolved sophisticated neural machinery specialized in impact reduction.

  • For example, a forefoot strike landing is the predominant foot strike in habitual barefoot runners and is a neural adaptation due to heightened proprioceptive responses. This implies that forefoot running has a long evolutionary history and was used to reduce impact over the wobbling mass effect.
  • The wobbling mass effect is essential to a small degree, but is also counterintuitive because it is an energy leak. Forefoot running plays a more important role in how the body reduces impact because impact peaks are eliminated, therefore wobbling mass response is minimal.

Ironically, most of the research on the wobbling mass effect pertains to heel strike running since impact peaks and joint loads are greater compared to forefoot running. Therefore, it is of great interest to understand how the body copes with these high forces.

In contrast, studies on the wobbling mass effect in forefoot running are less likely to be published because the lack of high impact is a well-established property of forefoot running.

In conclusion, the current study’s findings imply that forefoot running is a more rewarding, impact reducing strategy, that keeps impacts below biologically tolerable limits, thereby saving energy because less physiological effort is needed for muscle suspension.

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References:

Blickhan, R., Seyfarth, A., Geyer, H., Grimmer, S., Wagner, H., Günther, M.: Intelligence by mechanics. Philos. Trans. Ser. A Math. Phys. Eng. Sci. 365(1850), 199–220 (2007)

Boyer, K.A., Nigg, B.M.: Soft tissue vibrations within one soft tissue compartment. J. Biomech. 39(4), 645–651 (2006)

Boyer, K.A., Nigg, B.M.: Quantification of the input signal for soft tissue vibration during running. J. Biomech. 40(8), 1877–1880 (2007)

Davis, B.L., Cavanagh, P.R., Sommer, H.J. III., Wu, G.: Ground reaction forces during locomotion in simulated microgravity. Aviat. Space Environ. Med. 67(3), 235–242 (1996)

Günther, M., Sholukha, V.A., Keßler, D., Wank, V., Blickhan, R.: Dealing with skin motion and wobbling masses in inverse dynamics. J. Mech. Med. Biol. 3(3/4), 309–335 (2003)

Järvinen, T.L., Kannus, P., Sievanen, H., Jolma, P., Heinonen, A., Järvinen, M.: Randomized controlled study of effects of sudden impact loading on rat femur. J. Bone Miner. Res. 13(9), 1475–1482 (1998)

Jorgensen, L., Crabtree, N.J., Reeve, J., Jacobsen, B.K.: Ambulatory level and asymmetrical weight bearing after stroke affects bone loss in the upper and lower part of the femoral neck differently: bone adaptation after decreased mechanical loading. Bone 27(5), 701–707 (2000)

Schimitt S and Gunther M. Human leg impact: energy dissipation of wobbling masses. Arch Appl Mech, 2011; 81:887-897.

Taaffe, D.R., Robinson, T.L., Snow, C.M., Marcus, R.: High-impact exercise promotes bone gain in well-trained female athletes. J. Bone Miner. Res. 12(2), 255–260 (1997)

Wakeling, J.M., Liphardt, A., Nigg, B.M.: Muscle activity reduces soft-tissue resonance at heel-strike during walking. J. Biomech. 36(12), 1761–1769 (2003)

Bretta Riches

Bretta Riches

"I believe the forefoot strike is the engine of endurance running..."

BSc Neurobiology; MSc Biomechanics candidate, ultra minimalist runner & founder of RunForefoot. I was a heel striker, always injured. I was inspired by the great Tirunesh Dibaba to try forefoot running. Now, I'm injury free. This is why I launched Run Forefoot, to advocate the health & performance benefits of forefoot running and to raise awareness on the dangers of heel striking, because the world needs to know.
Bretta Riches

P.S. Don't forget to check out the Run Forefoot Facebook Page, it's a terrific place to ask questions about forefoot running, barefoot running and injury. I'm always happy to help!

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