Personal Bests: These are the changes to concentrate on if you want to produce more PBs.
In the first installment of our series of articles on improving your running form ('Be a Better Runner without Higher Fitness - with the Right Form,' PP, March 1997), we mentioned THE inescapable fact about running-form changes and performance: if you're going to make alterations in your form in order to run faster, those changes must lead to either a quickening or elongation of your strides. If your stepping is neither faster or longer, your form make-over may make you look prettier, but it won't move you even one step toward a new PB.
Somewhat paradoxically, as you breeze along toward your PB, you will probably still be moving at the same percentage of VO2max as always; it's just that that percentage is now 'owned' by a faster speed. Maybe you used to run 6:30 per mile at 95% VO2max intensity in your 5-K races, and now you can handle 6:15 pace at 95%. Whatever the actual numbers, your improved biomechanics allow you to move more swiftly without actually occurring additional physiological cost or added mental perception of effort.
What kind of form changes should you try to make? In our first article, we mentioned that 'form detectives' have often focused on the biomechanical changes associated with ageing in order to find clues about what constitutes good form. That makes pretty good sense, since both form and speed change simultaneously with age. It's quite reasonable to think that biomechanical downturns are at least partially responsible for the increased sluggishness in performance which is associated with ageing. Perhaps the form differences between young and old runners are similar to the disparities observed between fast and slow performers.
Age shortens stride length
One of the best of the biomechanical sleuths has been Nancy Hamilton of the University of Northern Iowa, who has shown, somewhat surprisingly, that stride rate doesn't change much with age, while stride length decreases drastically. For example, runners in their seventies have strides which are only 79 per cent as long as runners in their thirties, although their stride RATES are quite similar. To put it another way, as you get older your feet strike the ground just as frequently as they did when you were a kid; you slow down because you cover less ground between strikes.
Support time (the actual amount of time the right or left foot remains in contact with the ground during each stride), deteriorates even more badly than stride length, swelling by 25 per cent in 70-year-olds, compared to 30-year-old runners. That's bad, of course, because the support phase of the gait cycle represents the time when a runner's body is 'screwed into the ground' and is not moving ahead. To improve your performances, what you actually want is LESS support time and - within reason - more 'air time,' because the flight portion of the gait cycle is the only time that you actually make progress across terra firma. In Hamilton's study, flight time dropped by up to 30 per cent as support time increased; older athletes were spending more time attached to the ground and less time flying from one foot to the other ('Changes in Sprint Stride Kinematics with Age in Master's Athletes,' Journal of Applied Biomechanics, vol. 9, pp. 15-26, 1993).
This suggests that older runners were not reacting quickly enough when their feet made contact with the ground, and that they were spending too much energy stabilising their bodies after their feet hit the earth - and too little energy 'exploding' forcefully toward the next footstrike. The slowness to react and the need for greater stabilisation chewed up time (expanding support time by up to 25 per cent), and the lack of explosiveness shortened air time and reduced overall stride length. Contact with the ground was more like a sad collapse than a forward detonation.
That's very interesting - and certainly suggests that older runners need to spend more time training their agility, coordination, reaction time, and power. Come to think of it, there's not a single distance runner who wouldn't benefit from upgraded nimbleness, motor control, and explosiveness. Of course, the way to achieve these fine things is to emphasise their development in a well-formulated 'block' of training, a period which would follow on the heels of overall strength development and which would include such activities as hill running, weighted-vest training, speed bounding, and very fast reps on the grass or track (for convenience, we'll call this SHIRV training - for Speed bounding, HIlls, Reps, and Vest work).
Shooting from the hip
But how can one relate actual form changes to greater explosiveness - less support time and more air time? Well, Hamilton looked at three key biomechanical variables - range of motion (ROM) at the trunk, hip, and knee - to determine their association with running velocity. Surprisingly, only hip ROM was a good predictor of running speed: runners with the greatest ROM at the hip were the fastest competitors.
Why was that? According to Hamilton, the fastest runners have the greatest hip mobility during hip extension - the backward movement of the leg at the hip. Hip extension is the 'kick' or drive phase of running - when the foot becomes a rigid lever for toe-off, the gluteal and hamstring muscles recoil and contract to propel the leg backward, and the quads also activate themselves to help straighten the leg for the backward push. As this backward push becomes more powerful, hip ROM naturally increases, and movement occurs much more quickly (because the runner is rocketing through the air from foot to foot).
How do you enhance your hip ROM? Well, the kind of training we've described above (strength work, followed by SHIRV) can make a huge difference, but other factors are also important. Flexibility of the quadriceps muscles is one key to greater ROM, since overly tight quads will resist backward leg movements. Consistent and thorough stretching routines for the quads - carried out only after a thorough warm-up - can certainly help make the quads and their associated connective tissues more supple.
As we mentioned in our previous article, yet another key is to deliberately alter the way you run, eg, to focus intently on using the muscles around the buttocks to push backward. As Hamilton puts it, 'Rather than reaching out with the foreleg to increase your stride length, think about pushing back as hard as you can on each step. Use the buttocks and hamstrings to do so, very much the way you might push out hard from a set of starting blocks. Run from your hips - not from your knees'. Don't forget that a six- to eight-week emphasis on SHIRV will help give your glutes and hams enough puissance to really make a difference when they push you forward.
Although increased stride length is an important part of improved running, we should reinforce Hamilton's contention that you shouldn't artificially attempt to embolden your strides by reaching out for extra turf as you move along. The problem with such grasping is that it makes it impossible for your foot to land more or less under your centre of gravity. If your foot hits the ground ahead of your mass, a braking action is created which slows body movement and expands support time. Trying to reach out with your foot may also tend to make you a 'leaper'; you may end up squandering energy to lift your body too far off the ground vertically - so that your foot won't hit the ground 'too soon'. In general, increased vertical movements are less than optimal; research has shown that elite runners have less vertical change in their centres of mass during running, compared to average runners, and investigations have also shown that reducing one's quantity of vertical movement tends to improve economy ('Relationship between Distance Running Mechanics, Running Economy, and Performance,' Journal of Applied Physiology, vol. 63 (3), pp. 1236-1245, 1987). Surprisingly, speed bounding, because it emphasises quick-horizontal rather than vertical motion, is one technique which helps reduce up-and-down movements (speed bounding is just VERY fast running with longer-than-usual strides). Weighted-vest training also helps you learn to avoid hopping about like a jackrabbit.
In addition to increasing your hip ROM, reducing your vertical oscillations, and enhancing your explosiveness (achieving more air time and less support time), what other positive improvements can you make in the way you run? Although the research with ageing runners did not strongly correlate stride rate with performances, changing your stride frequency may actually help you a little, especially if you're currently a slow strider. Elite runners usually make impact with the ground about 180 to 200 times per minute - at all distances from 800 metres up to the marathon, while average runners tend to settle for 170 steps per minute or so (85 strides). Although the effects of practising increased stride rates haven't been studied carefully in a scientific setting, it's likely that learning to run with a footfall frequency of 180 or more can be helpful. It's relatively easy to do so: just count the number of times your right foot strikes the ground during a minute of your regular training or racing, and then multiply that number by two. If you're below 180, you can set your runner's watch to beep 90 times a minute and let your left or right footstrikes coincide with the beeps as you train.
A fair amount of the form research has done exactly what Hamilton did - examine joint angles during running and then correlate them with either performance or efficiency of movement. Not surprisingly, these investigations have shown that more acute (smaller) knee angles during the swing phase of running (when the leg moves back after toe-off and is then drawn forward for the next contact with the ground) are better than larger angles ('A Biomechanical Comparison of Elite and Good Distance Runners,' Annals of the New York Academy of Sciences, vol. 301, pp. 328-345, 1977). This basically means that your foot should be up by your buttocks during the swing phase and not dangling at some distance from your body, a fact which should be intuitively obvious to all runners: as you flex your knee and move your foot more towards your bum, you in effect create a shorter leg to move back and forth and thereby decrease the work which must be completed by your hip muscles, compared to what happens when your knee is less flexed and your extended foot must be swung through the air like a shod anvil. To put it another way, by placing less resistance on your hip muscles, you allow those muscles to work more powerfully, and you run faster.
Other research has shown that having a relatively straighter leg at toe-off (instead of maintaining greater flexion at the knee) is associated with better economy (Journal of Applied Physiology, vol. 63(3), pp. 1236-1245, 1987). Thus, it appears to be important to nearly eliminate knee flexion at the moment of toe-off - but then rapidly flex the knee for the subsequent swing stage of the gait cycle. Studies carried out by noted running biomechanicist Peter Cavanagh have shown that heightened plantar flexion of the ankle at toe-off and the rapidity of plantar flexion are also critical (Annals of the New York Academy of Sciences, vol. 301, pp. 328-345, 1977, and 'Biomechanical Correlates with Running Economy in Elite Distance Runners,' Proceedings of the North American Congress on Biomechanics, pp. 287-288, 1986). In plantar flexion, the toes move away from - rather than toward - the shin. Thus, the optimal anatomical position for toe-off seems to be a nearly straight leg with pointed toes.
Don't imitate Groucho
Over-flexion of the knee appears to be a bad thing in general during the stance phase of the gait cycle. As Hamilton points out, the leg must be straightened prior to toe-off, so having excessive flexion at the knee increases the time needed to straighten the leg and thus increases support time. Studies in which subjects have run with exaggerated knee flexion ('Groucho running') have documented a nearly 50-per cent increase in the energetic (and oxygen) cost of running ('Groucho Running,' Journal of Applied Physiology, vol. 62, pp. 2326-2337, 1987)!
What about the arms? While many runners, believing that the arms help propel them forward, use rather expansive arm swings, the research convincingly paints a different picture: More economical runners actually have less arm movement, compared to inefficient competitors ('Running Economy, Anthropometric Dimensions, and Kinematic Variables,' Medicine and Science in Sports and Exercise, vol. 26(5), p. S170, 1994). Quick little arm movements - in synchrony with the swings of the legs - are the ones which produce the most economical running.
Of course, economy is hurt by excessive motions of the upper body. Research has determined that as both the speed and amount of rotation of the shoulders and hips around the centre axis of the body increase during running, economy is harmed (ibid). Such wash-tub-like motions are controlled by the 'core' muscles of the body (the muscles of the upper torso which attach to the pelvic girdle and spine), bringing into focus once again the importance of utilising core exercises to promote efficiency.
The bottom line? There are lots of possible changes you can make in your running form, but not all of them will produce improvements in economy and performance; in fact, some may actually make you less efficient. One of the worst things you can do is to simply decide that you need to take longer strides - and then begin reaching out for more turf as you train. If you attempt to take longer steps in your workouts and races, you will probably hurt your economy rather than help it. Expansions of stride length are good, but they should occur the natural way - by improving your coordination, flexibility, and explosiveness, not by making naive adjustments in your running style.
To summarise, the research on running form suggests the following: Increasing hip ROM by swelling leg extension is a good and necessary part of becoming a faster runner. To do so, you must increase the power of your glutes and hams (through SHIRV training) and mentally focus on pushing backward with each footfall.
If you're below 180 steps per minute, increasing your stride rate is also probably good, and reducing vertical oscillations while running is definitely a fine thing to do. You also want less knee flexion during the support phase of running, and you want to shoot for a pretty straight leg at toe-off. In contrast, you should look for MORE flexion at the knee during the swing phase, so that your hip muscles don't have to throw too much foot-weight around.
And remember that your arm movements should be minimal, and that excessive upper-body rotation and rocking will cost you too much energy (you must strengthen your core!). Finally, don't forget that strength and SHIRV training will make you stable and powerful enough so that many of your concerns about form will diminish. As your form improves, you'll begin running economically and quickly to some new PBs.
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