February 18, 2019

“Science is the attempt to make the chaotic diversity of our sense experience correspond to a logically uniform system of thought.”

Albert Einstein

‘Overstriding’ (foot position on initial-ground contact too far forward relative to the runner’s general centre of mass) is widely accepted within the sports medicine community as a risk factor for running injury and poor performance. The established coaching solution is to increase stride frequency using a metronome to a cadence of 180bpm. The latest research by Dan Lieberman and his team at Harvard attempts to qualify ‘over-striding’ and quantify the effect of changing stride frequency on impact peaks and running economy.

1. OVERSTRIDING AT THE HIP

  • Caused by excessive hip flexion
  • Increases as cadence decreases
  • Creates increased braking force
  • Increased joint torques at ankle, knee, hip and sacroiliac joint

We considers the primary cause of this type of ‘over-striding’ to be chairs and habitual seated postures.

2. OVER-STRIDING AT THE KNEE

  • Caused by excessive knee extension
  • Creates increased GRF impact peaks
  • Consequently disproportionate Increase of joint torques at knee = increased risk of knee injury

We considers the primary cause of this type of ‘over-striding’ to be cushioned shoes.

3. ECONOMY: STRIDE RATE V. OVER-STRIDING

The metabolic cost of ‘swing phase’ is primarily due to Maximum Hip Flexion Moment (MHFM) i.e. the muscle activity required to overcome momentum and create the ‘swing’.

The metabolic cost of an ‘over-stride’ is due to the braking impulse that decelerates the body during the first half of stance i.e. the muscle activity required to counteract gravity and Ground Reaction Force (GRF) 

Dan’s study found that 170 seems to be the average energetic optimum when running at a speed of 3.0ms on a treadmill

We considers the ‘sweet spot’ to be a stride frequency of 170-185 in SKILFUL runners. The stride frequency varies within this range due to speed, body weight, age and terrain.

References:

Lieberman, D.E., Warrener, A.G., Wang, J. and Castillo, E.R. (2015). Effects of stride frequency and foot position at landing on braking force, hip torque, impact peak force and the metabolic cost of running in humans.Journal of Experimental Biology, 218, 3406-3414


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