Running economy

Page 1 2

Footstrike, rather than genetics, proves to be the answer
If you suggest a unique genetic configuration is behind the Kikuyu advantage, you are well off the mark: Maloiy also measured the energy expenditure of Luo women walking with weights, and they exhibited similar parsimony. There are probably over six million Kikuyus within Kenya and almost four million Luo, but Luo and Kikuyu rarely intermarry, and the two groups have dissimilar ancestral bases, so it would be difficult to imagine that both tribes have captured an identical super gene, or even some set of super genes.
Fortunately, Heglund has a different explanation. In research which followed the initial explorations of Kikuyu economy, Heglund and his friend Giovanni Cavagna of the University of Milan asked two women to carry loads Kikuyu style (with straps on their heads), two to carry loads Luo style (with weights directly on their head), and one to use both styles of support. For comparison, six male and six female Europeans carried similar loads in backpacks. All individuals walked across a force platform mounted at ground level in the middle of a walkway with and without the loads, and gravitational potential energy and kinetic energy were measured from the measured forces (5).
Heglund and colleagues focused closely on the conversion of kinetic energy to potential energy and back again during the various walks. Interestingly, the ability to convert energy back and forth without losing it increased with increasing load in the African women, explaining why they could carry extra weight without increasing their basic energy expenditure. Under normal circumstances, walking individuals can preserve about 65% of their total energy of movement per step, but the African women could hold onto over 80% of their movement energy as their loads increased to 20% of body weight.
How did the women manage to be so efficient? According to the researchers, the answer can be found in what happens during footstrike. As individuals move through the 'top' of one stride (remember the pendulum analogy; the top of the walking stride is when the centre of mass reaches its greatest height and potential energy attains its maximum) and start to fall into the next step, most pause for a few milliseconds before beginning to fall. Muscles in the legs are contracting and fighting the fall, trying to preserve balance. This decelerates the body (causing a loss of energy during the potential-kinetic transfer) and, of course, increases energy expenditure.
By contrast, the Kenyan women shorten or eliminate the pause at the top of the stride. Thus, there is no added deceleration, no loss of potential energy, and no unnecessary increase in energy expenditure associated with muscular contractions (since the muscles aren't trying to exert a braking effect at the stride's top). The Kenyan women are, in effect, more perfect pendulums.
In effect, the Kenyan women eliminate braking actions during the footstrike portion of gait and thus improve their efficiency. As runners, we can do the same thing. If we take off the brakes and eliminate the pause during footstrike, we'll be better able to preserve potential and kinetic energy, and our energy cost - expressed as either calories or millilitres of oxygen per minute - will be lower. Since we'll be operating at a lower percentage of VO2max, our efforts will feel easier, and so we will be able to step up our training and race paces.
But how do we actually take the brakes off? Two factors must be at work: first, our nervous systems must be highly reactive, so that muscular actions which inhibit forward propulsion can be tightly controlled from the moment of impact, and muscular actions which boost propulsion can be instigated without hesitation. Second, our movements must be well coordinated, so that there is no need to spend extra time (and energy) restoring the body's equilibrium position. Footstrike must be an explosive time, not a period in which weakly controlled joint movements must be corrected prior to toe-off, or in which the leg muscles 'throw on the brakes'. What we want to achieve is speed and control.

Exercises that will improve that all-important footstrike
To dramatically enhance speed, abbreviate the duration of footstrike, and decrease energy wastage during the footstrike portion of walking and running, carry out the following routine several times a week.

1. Springy jogging: jog along with very springy, short steps, landing on the mid-foot area with each contact and springing upwards after impact. As you move along, your ankles should act like coiled springs, compressing slightly with each mid-foot landing and then recoiling quickly - causing you to bound upwards and forwards. Move along for one minute with quick little spring-like strides, alternating right and left feet as you would during regular running. After this minute is completed, jog in your regular manner for about 10secs, and then 'spring-jog' for about 20m, alternating three consecutive spring-like contacts with your right foot with three contacts with the left (eg three hops on your right foot, three hops on your left, three more on your right, etc, until you have travelled about 20m). Jog in your usual manner for 10secs again, and then spring-hop along for 20m on your right foot only, before shifting over to 20m on the left foot alone (making certain that you land in the mid-foot area with each ground contact).

2. One-leg hops on the spot: two sets of 40secs on each leg. Stand in a relaxed position, with your full body weight supported on your left foot only. Lift your left heel slightly, so that the force of body weight is passing through the ball of the left foot (your right knee is flexed so that your right knee is off the ground). Then, hop rapidly on your left foot at a cadence of 2.5 to 3 hops per second (25 to 30 foot contacts per 10secs) for the prescribed time period, while maintaining relaxed, upright posture. Your left foot should strike the ground in the area of the mid-foot and spring upwards rapidly, as though it were contacting a very hot burner on a stove. Your hips should remain fairly level as you do this; try to minimise vertical displacement of the upper body.

3. 'Box-hop' with 'sticks': for 60secs on your right foot, rest for a few seconds, and then shift over to 60secs of box hopping on your left foot. After resting for a moment, repeat with each foot. The box utilised for this exercise should be sturdy and about six inches in height. To perform the exercise, stand about two metres away from the box, and then hop forward quickly towards the box on one foot only. As you near the box, hop up onto the box surface (continuing to hop on only the chosen foot), and then hop quickly off the 'far' side of the box. When you land on the other side, hop forward explosively, ie with as little ground-contact time as possible. In this explosive hop, try to avoid significant vertical oscillation of your centre of mass; you are trying for length, not height. When you land from this explosive hop, continue hopping on the same foot for four more hops, and when your foot touches down after the fourth hop, 'stick' your position, ie stop movement completely while remaining relaxed and nicely balanced on your single foot. Jog back to the starting point on both feet, and then continue the exercise on the chosen foot until the time limit is up. Following a short rest, do the hopping routine on the other foot.

4. High-knee explosions: complete 10 with your right leg, rest for a few seconds, and repeat with your left leg. To carry these out, stand with erect but relaxed posture with your full body weight supported on your right foot. Begin by jumping very lightly on the spot on your right foot only, but then suddenly - while maintaining fairly erect posture - jump vertically while swinging your right knee up towards your chest (your left arm should swing forward as your right knee comes up). Land back on your right foot in a relaxed and resilient manner, jump lightly for a few moments, and repeat nine more times, before resting briefly and continuing the pattern on your left leg.

5. Shane's in-place accelerations: to carry these out, stand with erect but relaxed posture with your feet directly below your shoulders. Begin by simply jogging on the spot, but then - when you feel ready - begin to dramatically increase your in-place 'stride rate', building up fairly quickly to as rapid a rate of striding as you can sustain (remember that you are not moving forward to any significant degree). Keep your feet close to the ground as you do this; you're not shooting for high knee lift but rather for dramatically minimised foot-contact times. Maintain erect but relaxed posture. As you accelerate up to 'top speed', it sometimes helps to turn your legs slightly outwards at the hips. Perform 3 x 20secs.

To minimise the risk of injury, at least at first, please make sure that all of these activities are completed on a 'forgiving' surface (soft dirt, grass, cushioned artificial turf, or wooden gym floor).
This group of quicksilver exercises will, of course, enhance the reactivity of your nervous system and thus help to minimise footstrike time. Naturally, strength and coordination of the weight-bearing leg are also needed to ensure that energy will not be wasted correcting non-optimal leg and body movements associated with footstrike. As mentioned, the overall idea is to create quick-to-act legs which channel all available energy towards forward propulsion, without the need to correct anti-propulsive movements. Towards that end, the following exercise strengthens the legs tremendously and improves balance and coordination to a close-to-maximal extent.

Partial Squats: one set per leg. Stand with your left foot directly under your left shoulder, keeping your left knee just slightly flexed and maintaining relaxed, fairly erect posture. Hold the barbell (initially with no weights attached) so that it rests on the top-back of your shoulders just behind your neck; you may incline your upper body just slightly forward for balance. Most of your body weight should be directed through the heel to mid-portion of your left foot. Your right leg should be flexed at the knee so that the foot is not touching the ground at all - your right foot is literally suspended in air (although, you may occasionally need to 'spot-touch' the floor for balance with your trailing leg).
From this position, if you were carrying out a traditional one-leg squat you would ordinarily bend your left leg at the knee and lower your body until your left knee reached an angle of about 90 degrees between the backs of your thigh and lower leg (usually at this point your thigh would be almost parallel with the ground). However, for the partial squat you should just go down about half-way - so that the angle between the back of your thigh and lower leg is just 135 degrees or so. Then return to the starting position, maintaining upright posture with your trunk. That's one rep!
So far so good - but you have lots more work to do! Continue in the manner described above until you have completed 10 reps (10 partial squats). Then - without resting - descend into the 11th partial squat, but instead of rising back up hold the partial-squat position (the 135-degree position) for 10 full seconds. We'll call your body alignment during this 10-second period the 'static-hold' position.
After completing 10secs in the static-hold position, immediately - without resting - rattle off 10 more reps, maintain the static hold on the 11th rep for 10secs again, hit 10 more reps, and then hold statically for 10 more seconds on the 11th rep. That's one set!
To summarise, a set proceeds as follows (with no recovery at all within the set):
(A) 10 partial squats
(B) 10 seconds of holding your leg and body in the down position
(C) 10 partial squats
(D) 10 seconds of holding
(E) 10 partial squats
(F) 10 seconds of holding

If you complete these six exercises two to three times a week and emphasise intensity of effort in your regular walking or running training, you will soon develop springy, explosive legs which refuse to dawdle during footstrike and put all available energy into moving you forward. Soon you'll be moving more efficiently, like a Kikuyu woman, even if you are a white male. The good news is that such efficient movements will make you a truly faster runner, whether you are a soccer player, rugby enthusiast, basketball player, cricketer, or marathon runner.

Owen Anderson

« back