Leg strengthening exercises

These one-leg strengthening exercises spell greater power, but you have to do them fast

In ‘How to improve your performance by optimizing the functioning of your nervous system’, I explained why athletes should focus on strengthening movements, not muscles, and why individuals, both runners and those whose sport involves running, who want to improve their running prowess should funnel their training energies toward ‘one-leg’ resistance exercises which mimic the mechanics of running. In this follow-up article, I want to discuss the special properties of one-leg exercise and describe why athletes should pay special attention to the speed with which their strengthening activities are performed.

To begin with, I should point out that proponents of one-leg over two-leg weight-bearing exercises often make two key arguments: (1) Utilizing one-leg exercises during training does a much better job of improving coordination and efficiency during one-leg activities like running, compared with two-leg exercises. (2) Since full body weight must be supported by one leg rather than two during one-leg activities, force production in the muscles of the involved leg increases dramatically, thus producing a considerably greater strengthening effect.

But by how much does leg-muscle activation increase when one shifts from two-leg to one-leg activities? In one study in which subjects performed maximal leg extensions, the average force produced in one-leg performance was 23-per cent greater than the force produced by the same leg during maximal two-leg work (‘Contralateral Influence on Recruitment of Curarized Muscle Fibers during Maximal Voluntary Extension of the Legs,’ Acta Physiologica Scandinavica, vol. 103, pp. 456-462, 1978).

In another study, activation level of the quadriceps muscles during leg extensions was from 27 to 116 per cent (!) higher at various extension velocities when the activity was carried out in one-leg fashion rather than two (‘Comparison of Motor Unit Activation during Unilateral and Bilateral Leg Extension,’ Journal of Applied Physiology, vol. 56, pp. 46-52, 1984). The ‘knock’ against these two pieces of research has been that the actual exercise utilized – leg extensions – is not a complicated, dynamic, or weight-bearing activity. Would the same kind of results be obtained during complex motor activities involving high degrees of coordination, such as running and jumping?

Enter the Dutch volleyballers
To answer that question, researchers at the Free University of Amsterdam studied 10 well-trained male volleyball players who warmed up thoroughly and then performed a number of vertical jumps with preparatory counter-movements, using the left leg alone for some jumps and both legs simultaneously for others (for the left-leg jump, the right leg was held inactively under the body). As the athletes carried out their jumps, I EMGs were recorded from the key muscles of the legs (‘A Comparison of One-Legged and Two-Legged Countermovement Jumps,’ Medicine and Science in Sports and Exercise, vol. 17(6), pp. 635-639, 1985).

The decision to utilize the left legs of the athletes was a particularly good one. Leg circumferences (i.e., leg-muscle sizes) were smaller in the left legs,than in the right ones, so it was likely that the left legs of the athletes were the weaker, non-dominant ones. Thus, if power output happened to be greater in the left leg, compared with average power production for the two legs, it would have to be the result of unique aspects of one-leg activity, not merely a reflection of the greater strength of a dominant leg.

Naturally, mean jumping height during the one-leg jumps was lower than that achieved during the two-leg efforts. Interestingly enough, however, jumping height in the one-leg case was significantly greater than 50 per cent of the two-leg height, averaging 58.5 per cent. In effect, the left leg acting alone was producing a higher jump than the mere average of the two legs acting together (i.e., total jump height divided by two), even though the left leg was the more impoverished appendage! In fact, total work carried out per leg per jump was about 16-per cent greater in the one-leg case.

What happens to the ankle joint
Interestingly, the Dutch scientists were able to show that one-leg and two-leg jumping produced significantly different effects on the ankle joint. Specifically, the ‘minimal angle’ attained by the ankle during the countermovement (squatting motion) prior to the jump was smaller during the one-leg jump, compared to the two-leg effort. The minimal angle is simply the angle between the top of the foot and the shin, which means that during one-leg jumping significantly more dorsiflexion of the ankle was permitted. Not surprisingly, in the one-leg jump both peak and average power outputs were greater in the ankle joint than they were during the two-leg jumps, i.e., the calf muscles had to work generally harder and more powerfully to control and respond to the greater magnitude of dorsiflexion during counter-movement. It would not be too great a ‘stretch’ to suggest that the magnitude of the gain in ankle strength should be greater after a period of one-leg jump training than after two-leg efforts.

These three studies indicate that during two-leg activity it is usually impossible to reach the levels of neural activation and force production which can be attained during one-leg exertion. When one also takes into account the coordination effect mentioned earlier, it becomes difficult to understand why athletes engaged in sports which involve running would prefer two-leg and seated activities over one-leg exercises.

Where’s the speed?
So far, so good! I’ve shown you exactly how to produce the right neural adaptations for running and thus maximally heighten your running-specific strength (in case you’ve already forgotten, the idea is to stress one-leg movements which mimic the mechanics of running in at least some key way). If you strength-train in the right way, you’ll be able to take longer strides when you run, you’ll be less prone to injury, you’ll climb hills like a mountain goat, you’ll run farther than you ever could before, and you could finish the London Marathon with a sack of rocks on your back.

 Of course, all of that is great, but there’s just one little problem: you won’t necessarily be a faster runner. If you think that longer stride lengths automatically make you faster, think again – greater stride lengths are sometimes associated with a longer stance phase in the gait cycle (the increased amount of time with the foot on the ground gives the leg muscles more time to pile up force, thus elongating strides). If stride length increases but stride rate declines (because of swollen footstrike times), you are not necessarily faster.

Thus, to be a significantly faster (i.e., more powerful) runner, you should not only generate more force but generate that extra force more quickly (i.e., increase stride length and abbreviate footstrike time). You must work on your rate of force production.

To cut a long story short, to enhance your rate of force production while running, you must of course emphasize high-quality running training, and you must also be certain that the speeds of movement you select for your strengthening exercises begin to approach the speeds of movement characteristic of running. Otherwise, the strength you gain from your resistance exercises might carry over very well to slow running speeds – but transfer poorly to faster ones.

What happened in Sweden
If you doubt that this is the case, consider research carried out recently at the renowned Karolinska Institute in Stockholm, Sweden, in which Swedish athletes were randomly assigned to groups undertaking either eccentric or concentric exercise of their quadriceps muscles (‘Specific Effects of Eccentric and Concentric Training on Muscle Strength and Morphology in Humans,’ European Journal of Applied Physiology, vol. 79, pp. 49-57, 1998).

The subjects were tested and trained on an isokinetic dynamometer while in a seated position, restrained by straps over the upper thigh, pelvis, and trunk. The concentric-group members exercised by extending one leg at the knee, pushing maximally on the resisting lever arm of the dynamometer as the leg straightened (the lever arm was attached to the lower part of the leg with a pad). These were concentric contractions – the quads shortened as they flexed the leg at the knee. In contrast, the eccentric-group athletes maximally resisted the movement of the lever arm as it relentlessly flexed the leg at the knee (thus, the quads were engaged in eccentric activity, lengthening even as they exerted maximal tension against the remorseless lever). During both the concentric and eccentric actions, actual angular velocity of movement was kept constant (isokinetic) by the dynamometer. One velocity of movement (90 degrees per second) was utilized during training, and three velocities (30, 90, and 270 degrees per second) were utilized to test for gains in strength at the ends of the training periods. Total range of motion per eccentric or concentric action was always 85 degrees (between knee angles of 90 and 5 degrees, with 0 degrees representing a perfectly straight leg).

All subjects trained three times a week for a total of 20 weeks. Only the left leg was trained during the first 10 weeks of the study, with the right leg going through training over the final 10 weeks Each workout consisted of four sets of 10 consecutive maximal actions (either concentric or eccentric), with a two-minute rest between sets. As mentioned, training velocity was set at 90 degrees per second, which meant that every action (eccentric or concentric) lasted about one second, with one second of rest during the passive return of the dynamometer arm to the beginning position. During training, the non-active leg hung passively from the dynamometer seat. Before the training period began, the two groups were identical in terms of concentric and eccentric strength.

And the results?
After 10 weeks, the eccentric training had a dramatic impact on maximal power during eccentric activity, with peak torque increasing by up to 43 per cent at 90 degrees per second and 17 per cent at 30 degrees per second (note the specificity-of-training principle at work here; the subjects trained at 90 degrees per second, and therefore the increase in strength was greater at 90 degrees per second than at the slower movement speed of 30 degrees per second). The story was similar in the concentric group: peak torque increased by 20 per cent at 90 degrees per second but by only 13 per cent at 30 degrees per second.

Interestingly enough, in no case (either concentric or eccentric) did strength improve at 270 degrees per second. In other words, the training velocity utilized (90 degrees per second) produced the greatest gains in strength for both the eccentric and concentric groups, when the test velocity was set at 90 degrees per second. Both groups also improved – although to a lesser extent – at the slower velocities, but neither group was able to upgrade strength at high speed. Lesson: If you want to be stronger at high rates of movement, you must carry out your resistance exercises at high rates of movement, too.

Those crazy, control legs
Now that you know something about how the nervous system determines strength, you should not be surprised about this: in the Karolinska study, the ‘control legs’ (i.e., the legs which didn’t exercise at all) were able to improve their strength somewhat during the training periods, too. For example, after the first 10-week period, during which the right legs did no work at all in either the eccentric or concentric groups, peak torque during eccentric activity at 90 degrees per second advanced by 16 per cent in the right legs of eccentric-group members! Similarly, peak torque in the non-exercised right legs of concentric-group members increased by 10 per cent at 90 degrees per second! This shows us once again that there is this small thing called the nervous system which plays an important role during strength development.

Very interestingly, these gains in strength made by the non-exercised legs had a pronounced specificity. That is, the sedentary right legs of the eccentric-group members improved eccentric strength after 10 weeks only at the specific velocity – 90 degrees per second – utilized during the strengthening of the left legs, and there was no gain at all in concentric strength. The same was true in the concentric group, with the potato-couch right legs bolstering concentric strength only when the speed of movement was set at the familiar (for the muscles of the left leg and nervous system) 90 degrees per second; there was no upswing at all in eccentric strength.

Since gains in muscular strength are speed-specific, it follows that the athlete who runs at a higher speed during training is going to be stronger, and thus more fatigue-resistant, than the athlete who trains at slower velocities when the two are running at race-type paces. The athlete who trains at slower velocities may be more fatigue resistant at slow running speeds, especially if the slow velocities are combined with a high volume of training, but this has little importance in competitive situations, unless we are talking about ultra-marathons.

Owen Anderson