The Dance with the Devil: putting the steps together

Preamble

In the last three posts, I have attempted to describe what happens in the various stages of the gait cycle. However, the cycle is one integrated sequence, so this post will focus on how it all fits together, and including some detail about the torso and arms

Torso

Gordon Pirie recommends upright torso; Pose recommends a forward lean maintaining a straight-line from point of support via hips to shoulders, at mid-stance. The theory behind the Pose lean is based on what I believe to be false biomechanics. The proposal by Dr Romanov that gravitational torque can generate forward propulsion even when running at constant velocity is tempting, but violates the law of conservation of angular momentum. Subjectively, the lean can feel helpful – but I think that is a misleading perception based on the experience of starting from a stationary position. There is no doubt that a lean promotes acceleration that is helpful for a sprinter driving from the blocks, but acceleration is only a very minor part of longer distance running. So whose advice is more helpful: Pirie or Romanov? In a previous post I came down favouring Romanov, but that was after a session running into a strong wind. Maybe lean helps when you need continuing reinforcement of the horizontal drive on account of wind, but I am now inclined to think that Pirie’s advice is best on a level surface when the wind is not too strong.

The reason I think an upright torso is best is that it promotes a greater eccentric stretch of the hip flexors during late stance, and this will facilitate hip flexion after lift off, thereby bringing the leg forwards to overtake the torso by mid-swing. Upright torso also likely to promote effective deceleration of the leg by hamstrings and gluteus maximus in late stance, and good coordination of hamstrings and quads to achieve the required flexion of hips and knee at footfall. Both the quads and hamstrings cross hip and knee, and appear to have evolved so that despite being mutual antagonists, simultaneous contraction of both can produce well coordinated movements at both joints when the torso is upright.

Similarly, keeping the hips forward (i.e. avoiding ‘sitting in the bucket’) promotes more efficient hip flexor stretch in late stance which helps get the legs forward quickly; and promotes good coordination of the hip and knee at footfall.

Arms

When the neurosurgeon Wilder Penfield used electrodes applied directly to the brain to stimulate muscle contraction, as part of pre-surgical exploration of brain function in patients needing surgery for epilepsy at the Montreal Neurological Institute in the 1930’s, he demonstrated that a much larger area of the motor cortex in the brain is devoted to controlling the upper limb than the lower limb. This fits with the observation that most people are more dextrous with their hands than their feet. However, the upper and lower limbs automatically work in synchrony when running. So it is plausible that conscious focus on what we do with the upper limb will be more effective than focussing on the legs and feet. In particular, focus on the backward movement of the arm on the side of the leg that is beginning to swing in early swing phase is likely to help bring the leg forward in the optimum direction at the beginning of swing. Even more importantly, making sure that the subsequent forward swing of that arm does not go too far forward will promote the required (non-conscious) braking of the swing leg in late swing and minimize risk of over-striding. The harness proposed by Jack Cady of Stride Mechanics achieves this. This arm swing should be purposeful and controlled but not too tense to avoid wasteful isometric contraction in the shoulders. I find it helpful to form a lightly held ring-shape by resting the index finger of each hand against the adjacent thumb. I think this fairly delicate action encourages a controlled but relaxed arm. This recommendation for hand posture is attributed to Emil Zatopek, the great distance runner of 1950’s, who was famous for his contorted neck and facial features while running, but nonetheless, managed to maintain remarkable relaxation of his limbs (see Wikipedia entry for Emil Zatopek).

Rotation about the long axis of the body

As the hip extends in late stance, the hip rotates externally, thereby producing eccentric stretching of the internal rotators. At lift off, the hip rotates internally bring the leg around and forwards, thereby lengthening the stride and ensuring that the foot is in the midline by foot-fall. This rotation is facilitated by a balancing rotation of the upper torso produced by arm swing.

Integration

Assembling the main features from the previous postings, together with these principles regarding the upper body leads to the following integrated picture:

1) Cadence should be high (e.g. in the range 180-200 strides per minute) to minimise work required to overcome gravity in the airborne phase.

2) Time on stance should be short, though there is a balance between peak mechanical efficiency achieved with a time on stance around 50-60 milliseconds) and minimization of risk of tissue damage (maybe best achieved at around 100-120 milliseconds on stance. Short time on stance minimizes braking in early stance

3) Torso should be held near to upright, with perhaps a slight forward lean if needed to counter wind resistance.

4) Arms should swing in a relaxed but controlled manner, avoiding swinging too far forwards.

5) At foot fall, the hip and knee should be slightly flexed and the ankle near neutral, but with very sight plantar flexion to that the initial point of contact is on the outside edge just forward of mid-sole. As speed increases, the degree of flexion of the hip and knee should decrease making the leg stiffer, leading to a more rapid recoil and shorter time on stance. However, this will increase stress on musculo-skeletal tissues. It should be noted that many elite athletes actually land on the heel. This will result in an even stiffer leg, which may enhance mechanical efficiency, but the risks of over-striding and of musculo-skeletal damage are likely to be higher.

6) In mid-stance, contraction of the hip abductors prevents the hip dropping on the unsupported side, allowing the leg to swing freely and avoiding sideways slanting of the torso.

7) In late stance, recoil aided by contraction of the quadriceps will generate the vertical Ground Reaction Force that provides the impulse required to lift the body. Extension of the hip will preload the hip flexors.

8 ) A conscious pull using hamstring promotes a well-timed lift-off, and an associated concentric contraction of hip flexors in early swing brings the leg forwards to overtake the torso by the time the other leg is at mid-stance.

9) Rotation about the vertical axis of the body, produced by synchronised concentric contraction of the hip rotators with arm swing, will help open up the stride, and ensure that the support foot lands on the midline.

10) In late swing, gluteus maximus and hamstrings decelerate the leg so that horizontal velocity relative to the ground is near zero at footfall.

The next section of the Dance with the Devil will tackle the issue of the perceptions that allow us to achieve these actions effectively, and the mental state that prepares us for peak performance.

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