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Of mice and men

If that makes it seem like humans are energy wastrels during running, bear in mind that it could be much worse. For example, mice run with an efficiency of only 3%, which may help to explain why they seem always to be looking for food. Generally, larger animals (like humans) tend to be a little more efficient during running than small animals like mice, for reasons that are not exactly clear. The real paradox is this, however: when muscles are stripped from the legs of freshly killed mice and tested in the laboratory, they operate with an efficiency of 25%. That same experiment can obviously not be carried out with humans, but it is known that when humans ride bicycles, their efficiency is also about 25%. Why is running such an inefficient process for mice and so efficient for humans? When mice run marathons, their efficiency of movement drops from 25% to just 3%, while for humans efficiency during running soars from the 25% achieved during biking to 50%! The answer to the mouse question is unknown, but the key to the human running response is obvious. Each time a human foot hits the ground while running, energy is stored as ‘elastic strain energy’ by the key ‘springs’ in the human leg – mainly the connective-tissue strips which run along the bottom of the foot, the Achilles tendon and its associated muscles, the relevant muscles and tendons around the knee and the relevant muscles and tendons surrounding the hip. All of these structures are stretched when the foot hits the ground, and this stretching process stores energy – i.e. increases the potential energy of the leg. When the structures recoil elastically during toe-off, they manage to return about 90% of the work required to stretch them (with only 10% lost as heat). If the tendons and muscles of the leg were not able to store energy during impact with the ground, the muscles would have to increase their work output and energy expenditure dramatically. In fact, Alexander estimates that when humans run at middle-distance speeds, the spring-like properties of the Achilles tendon and the arch of the foot alone cut the work the leg muscles have to do by half. Here lies the answer to our paradox: human leg muscles are still working with only 25% efficiency during running; they do not really become more efficient just because running is the chosen sport. If the mechanical cost of movement is two joules per kg body weight per minute, half of this cost is furnished almost for free by the legs’ springs. Thus the muscles cough up four joules per kg per metre to provide the other joule per kg/metre of mechanical cost – with an efficiency of 1/4 = 25%.

The bottom line for you as an athlete who uses running in your chosen sport is that the best way to decrease your cost of running – and thus run faster and longer – is by enhancing the function of your leg springs. Since they are able to store energy more effectively when the foot hits the ground and then release this energy more fully and in a more timely fashion during push-off, your metabolic cost of running at a specific speed will drop, and you will be able to move up to higher speeds during training and racing. Fortunately, there are drills you can carry out to improve this ability to store and release elastic strain energy. Below are the key exercises for improving your springiness and thus your energy efficiency. Carry out these routines 2-3 times a week after a thorough warm-up, making sure you are rested and recovered from prior training. If your workout for the day contains a quality running component, perform the exercises after your warm-up and before the quality running and cool-down. Once you have completed the drills at least twice a week for six weeks or so, you may back down to once a week for up to 3-4 months as you work on other aspects of your overall fitness.

Exercises for enhancing springiness and energy efficiency

1. Spring-jogging

• After a nice warm-up, jog along with very springy, relatively 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, then recoiling quickly, causing you to bound upwards and forwards. Move along for one minute with quick, spring-like strides, alternating right and left feet as you would during normal running;
• After one minute, jog normally for about 10 seconds, and then ‘spring-jog’ for about 20m, alternating three consecutive spring-like contacts with your right foot with three contacts with the left (i.e. three hops on your right foot, three hops on your left, three more on your right etc until you have travelled about 20m);
• Jog normally for 10 seconds again, and then spring-hop for 20m on your right foot only, before shifting over to 20m on the left foot alone (making sure you land in the mid-foot area with each ground contact).

2. One-leg hops on-the-spot

• Stand with your left foot forward and your right foot back, with your feet about one shin-length apart from front to back and hip-width apart from side to side. Place the toes of your right foot on a block or step 6-8 inches off the ground and direct most of your weight through the mid-point of your left foot;
• Hop rapidly on your left foot at a cadence of 2.5-3 hops per second for 40 second. Your left knee should rise by about 4-6 inches with each upward hop, while your right leg and foot remain stationary. Your left foot should strike the ground in the area of the mid-foot and spring upwards rapidly, as if landing on hot coals. Your hips should remain as level and motionless as possible throughout the exercise, with very little vertical displacement;
• After hopping for 40 seconds on your left foot, shift over to your right;
• Take a short break, and repeat once more on each foot.

3. Box-hop with ‘sticks’

• Hop quickly up to the box on your right foot, then onto the platform and immediately off the opposite side;
• When your right foot hits the ground, react explosively – hopping forward as quickly as possible, resisting the temptation to let your ankle, knee, and hip flex dramatically and also the natural tendency to spend a lot of time on the ground before hopping forward. The movements should be smooth and quick at all times. Continue hopping for three more hops, and then ‘stick’ the final landing on your right foot, holding your body position, as a gymnast would do at the end of a routine;
• After a second or two of holding, run back to your original position, and repeat the series of hops;
• After 60 seconds, shift over to the same routine on your left foot;
• Rest for a moment, then repeat.
• Key points: maintain relaxed, upright body posture at all times and avoid looking at your feet or the ground as you hop along. Be sure to begin this exercise on a very forgiving surface – beach sand, soft dirt, soft grass or a relatively springy basketball court floor. Once you have built up considerable hopping strength, you may use harder surfaces.

4. Indian-hopping

• Jog for a few strides, and then take a jogging stride diagonally to the right with your right foot;
• When your right foot makes contact with the ground, hop once, then explosively hop diagonally to the left, landing on your left foot;
• When your left foot strikes terra firma, hop once, then explode diagonally to the right;
• Carry on alternating left and right in this fashion for 45 seconds. Rest for 15 seconds, then repeat. Stay relaxed at all times, moving in a coordinated and rhythmic manner and keeping the hops very springy and quick. Avoid the tendency to look at your feet.

5. One-leg squats with lateral hops

• Assume exactly the same starting position as in 2 above;
• Now, bend your left leg and lower your body until your left knee is bent at an angle of 90°;
• Then hop about 6-10 inches to the left on your left foot, keeping the right foot in place;
• Hop back to ‘centre’, then repeat on the other leg and return to the starting position, maintaining upright posture with your trunk and holding your hands at your sides;
• Perform 2 sets of 12 squats on each leg, with a one-minute break between sets.

6. High-knee explosions

• Stand erect but relaxed, with your feet directly below your shoulders;
• Begin by jumping very lightly on the spot, but then suddenly – while maintaining fairly erect posture – jump vertically while swinging both knees up toward your chest;
• Land back on your feet in a relaxed and resilient manner, then explode upwards again, aiming for as little time on the ground as possible while trying to maximise vertical jumping height;
• Complete 15 high-knee explosions, rest for a few seconds and repeat.

7. Shane’s in-place accelerations.

• Perform 3 x 20 seconds of Shane’s In-Place Accelerations. To carry these out:
• Stand as in 6 above;
• Begin by simply jogging on the spot, but then – when you feel ready – begin to dramatically increase your ‘stride’ rate, building up fairly quickly to as rapid a speed as you can sustain on the spot. Keep your feet close to the ground: you’re not going for high knee lift but rather for dramatically minimised foot-contact times – and an ability to get your feet to spring off the ground as soon as they make contact. Maintain erect but relaxed posture at all times. As you accelerate up to ‘top speed’, it sometimes helps to turn your legs slightly outwards at the hips until you become more accustomed to the exercise.
• Perform 3 sets of 20 seconds.

8. Hop sprints.

• At a park or on a decent track (resilient surfaces work best for this drill, especially initially), mark off a distance of 30 metres. Go to one end of the marked distance, then hop the 30m as fast as you can on your right foot, staying relaxed and trying to avoid excess vertical displacement of your centre of mass. Focus on two principles:
  1. push off as hard as you can each time the right foot hits the ground, but forwards rather than upwards
  2. make each stance phase (the amount of time your right foot is in contact with the ground) as short as possible. You are looking for very powerful, productive hops.

Once again, avoid the tendency to look downwards, keeping your gaze fixed ahead, as you would do during normal running.

After about four weeks of carrying out these exercises twice a week, you’ll begin to notice a real difference in your springiness and explosiveness, and after 6-8 weeks, the effects will be even more dramatic. You’ll begin to notice an increased springiness in your running strides, and you will also notice that high-quality running paces are beginning to feel easier.

Owen Anderson

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