Core stability training has become universally accepted as an integral and essential part of many sports conditioning programmes. But just how effective is it? Andrew Hamilton looks at the evidence MORE
Running training: how resistance work can improve efficiency and power
If you’re a regular reader of PP, you’ll recall that – in purely physiological terms – improved economy means using less oxygen to run at a particular pace. No, working on your economy doesn’t mean that you’re preparing yourself to compete in the first Mars Marathon; as your economy improves, you’ll still be dragging oxygen into your lungs and pushing it out to your leg muscles with your heart. It’s just that you need less of that life-giving gas to run at race-relevant speeds, which is great because it puts less pressure on your heart (which is glad to beat more modestly once it learns that your muscles don’t need quite as much oxygen as before) and makes running feel more effortless (there’s a direct relationship between oxygen consumption and perceived effort). As a result, a seemingly insignificant 2-per cent improvement in economy can carve a nifty 48 seconds from your 10-K time, if you’re currently about a 40-minute 10Ker.
So how do you actually improve your economy? Traditionally, exercise scientists have believed that strength training might do the trick. In part, the theory has been that strength work improves whole-body stability during the act of running. Thus, less energy is required to correct inappropriate movements (e. g., a wobbly trunk or an ankle which is dorsiflexed to too great a degree), and a particular pace can be sustained with a lower total energy cost.
Enter Hickson’s team
In the first study to explore the link between resistance training and economy, carried out at R.C. Hickson’s famous laboratory at the University of Illinois at Chicago, nine men (aged 18-27) took part in a 10-week, five-workout per week programme which was designed to strengthen their quadriceps muscles. The men were described as ‘active’ (e. g., participating regularly in recreational sports), but none were involved in long-term running or cycling training (‘Strength Training Effects on Aerobic Power and Short-Term Endurance,’ Medicine and Science in Sports and Exercise, vol. 12(5), pp. 336-339, 1980).
Three days per week, the subjects completed parallel squats (5 sets of 5 repetitions), knee flexions (3 x 5), and knee extensions (3 x 5). On the other two days, the men performed leg presses (3 x 5) calf raises (3 x 20), and a few dead lifts and sit-ups to fortify their back and abdominal muscles. All sets were separated by three-minute recovery periods. Although this programme may seem to be somewhat minimal, it wasn’t a complete piece of cake – because all of the exercises were performed with as much weight as possible. Initially, the resistance was set at 80 per cent of the one-repetition maximum (80 per cent of the maximal weight which could be lifted once and only once). As strength increased, additional weight was added to maintain this same relative resistance. The parallel squats and calf raises were conducted with Olympic-style weights, while the knee flexions, extensions, and presses were completed on a Universal Gym. At the beginning and conclusion of the study, strength was measured as the maximum amount of weight which could be lifted for one repetition.
The effect on cycling and running
The 10-week programme did have a dramatic impact on muscular strength, which burgeoned by 38 per cent for squatting, 42 per cent for knee flexion, and 50 per cent for knee extension. That was not a big surprise; the big shocker was that even though the subjects had not participated in a single cycling workout during the study, VO2max while cycling increased by 4 per cent after 10 weeks. However, VO2max during running was unchanged at the end of the 10-week period!
At the beginning and end of the 10-week study, the men took part in an interesting test of endurance: they tried to exercise for as long as possible at their initial VO2max (eg, the cycling intensity or running speed which produced VO2max at the beginning of the research). Of course, this meant they were cycling at an intensity a little below their true VO2max at the end of the study, since cycling VO2max had risen. Endurance time, as measured by this test, vaulted upward by 47 per cent on the bicycle (from 278 to 407 seconds) and increased by 12 per cent while running (from 291 to 325 seconds)!
Those large increases in endurance might seem a little unusual to you, especially since the subjects had not taken part in any cycling or running workouts during the research (the increases were certainly a puzzlement to Hickson and his crew, who could offer no real explanation for the gains). So, what should we conclude from this research? What caused the small increase in VO2max for the bikers? What caused the gains in endurance capacity during both cycling and running?
The easiest conclusion to draw is simply that strength training benefits cyclists and runners (to be more accurate, we should say that the study shows that strength training can help relatively inexperienced cyclists and runners who do not cycle or run regularly). We can also safely conclude that strength training of the type utilized in this study, with an emphasis on quadriceps strengthening, seems to benefit bikers to a greater extent, compared to runners (remember that endurance soared by 47 per cent during cycling, but just 12 per cent while running, and that VO2max increased only on the bike). While the caveat here is again that the athletes were inexperienced at cycling and running, the different responses should not be too surprising. The strength programme utilized in this research emphasized the development of quadriceps rather than whole-leg strength, and quadriceps power plays a much larger role in cycling than in running.
Unravelling the mystery
But what actually caused the hikes in cycling and running endurance? We can’t assign the laurels to VO2max, since running VO2max didn’t change at all, and cycling VO2max rose by only 4 per cent, a far cry from the 47-per cent lift in endurance. We also can’t pin our hopes on sweeter lactate thresholds, since blood-lactate levels during strenuous running and cycling were not different at the end of the study, compared to the beginning. The only other key physiological variable left is economy, which, although not actually measured by the researchers, was probably superior after the strength training. Bolstered quad strength, plus gains in the fortitude of the abdominal and low-back muscles resulting from the crunches and dead lifts, probably improved economy by stabilizing movement and thwarting energy wastage. This pushed the final bicycle test even further below the original cycling VO2max and made the run ‘at VO2max’ actually use less energy – and therefore oxygen – than a true at-VO2max effort. Thus, heart rate and perceived effort were substantially lower after 10 weeks, permitting the athletes to cycle or run at a high intensity for a considerably longer period of time than before they had undertaken strength training.
However, we should point out that in addition to promoting stability, improved strength probably enhances economy in another key way, too (we’ll use the cycling example to make our point). As mentioned, the individuals in the Hickson study could pedal for only 278 seconds (four minutes and 38 seconds) at their VO2max intensity when the research began. They then boosted their quadriceps strength dramatically over a 10-week period. This strength came not from growing more muscle cells in the quads but from strengthening the cells already present there. Since individual cells were stronger after the 10 weeks of strength training, fewer total cells were required to produce the force necessary to pedal at VO2max intensity, saving energy (and thus enhancing economy). The decrease in the number of cells required of course allowed some of the previously active muscle fibres to rest during activity. When the hard-working cells became fatigued during the endurance test, they could drop out of the action, but exercise could continue (the point of exhaustion was not yet reached), because the wearied cells could be adequately ‘replaced’ by the fibres which had been resting – and waiting for their chance to help. Putting it all together, we can say that increased strength not only aids economy by enriching stability and decreasing the number of muscle cells required to sustain activity; it also delays total fatigue by allowing collections of muscle cells to ‘share the work’ in an alternating fashion.
Answering the next question
If you’re getting into this article, you’re probably wondering why the delay in fatigue associated with increased strength was greater for cycling than it was for running. Shouldn’t improved strength be equally valuable in the two sports?
To answer that question, first bear in mind that the boost in strength was greatest in the quadriceps muscles, which are more important for cycling than running. In addition, the strengthening exercises utilized in the study (knee extensions, flexions, and presses while seated at a Universal Gym), were more specific to cycling than running, since they were carried out in a seated, non-weight-bearing position. In cycling, you are perched on your bum, as you are on the Universal Gym, and your legs seldom have to support full body weight, but that is certainly not the case while running! Thus the integrated actions of the leg muscles and the control and coordination of those muscles by the nervous system during the prescribed strength training were much more similar to the actions and control required for cycling, compared to running. As a result, the magnitude of the benefits carrying over to running were naturally smaller. When thinking about strength training, it’s important to remember that gains in strength are of course a function of enhanced muscle-fibre size, but they can also occur as a result of the nervous system’s ‘learning’ to coordinate muscle activity in the most power-producing manner possible. If both factors (better pure muscle strength, better coordination of muscles by the nervous system) are not working together, your strength training will never optimally improve your strength in your favoured sport. To put it another way, you can bolster your sinews in a variety of different ways, but you had better make your resistance training specific to your sport if you really want to achieve a performance-improving advance in your strength.
No, we haven’t forgotten about that other question: why did strength training boost VO2max on the bike? To put it simply, the strength upswing allowed the subjects to push against the pedals a little longer during the VO2max test (because each push represented a smaller fraction of total strength and was therefore more tolerable). The slightly longer duration of the test then got the athletes up to a higher oxygen consumption rate. As wise exercise physiologists like to say, you can almost always get to a higher VO2max – if your leg muscles will permit it!
In Hickson’s follow-up research (which also happened to be the second major published study on the effects of strength training on economy), the Illinois researchers eliminated one of the problems associated with their earlier research by involving experienced athletes in their work. All of the new subjects were already carrying out a regular running and cycling programme; on average, they ran three times a week and also cycled three times weekly – and continued to do so as they embarked on their new strength-training programme. Since the subjects were already so active, they strength-trained just three times per week in this second investigation (against. five times a week in the first piece of research). As in the first study, the subjects’ endurance capacities were tested during a very high-intensity, close-to-VO2max exertion, but they were also assessed during longer, submaximal efforts – either cycling at an intensity of 80 per cent of VO2max or running a 10-K race on an indoor track (‘Potential for Strength and Endurance Training to Amplify Endurance Performance,’ Journal of Applied Physiology, vol. 65(5), pp. 2285-2290, 1988).
Eight athletes (six men and two women) took part in this second investigation; their average age was 31, and they had above-average fitness (mean running VO2max was 60 ml/kg/min). The strength-training workouts were somewhat similar to the earlier ones, consisting of parallel squats ((5 sets of 5 reps), knee extensions (3 x 5), knee flexions (3 x 5), and toe raises (3 x 25), with two-minute recoveries between sets and 10 weeks of total training. As in the first study, as much weight as possible was utilized (if the subjects could perform more than five reps, additional weight was added). None of the participants had engaged in strength training during the six months before the study began, but – as mentioned – all had been carrying out regular running or cycling workouts and continued to do so as the strength training progressed.
Not too surprisingly, the resistance training had a significant impact on strength, advancing parallel-squat power by 27 per cent, knee-extension capacity by 37 per cent, and knee-flexion strength by 25 per cent. However, note that the gains in strength were not as great as in the initial investigation (in that study, strength had soared by 38 to 50 per cent). The reduced relative gains in strength may have been related to the fact that the second-study’s participants strength-trained just three times per week, instead of five. However, another key factor was that the second-study people possessed an initially higher level of strength, compared to participants in the first investigation, because of their long-term participation in running and cycling programmes.
Notably enough, VO2max did not increase, either while cycling or running, after the 10 weeks of strength training (in the first study, you’ll recall, VO2max while cycling had increased). As in the preliminary investigation, lactate threshold did not improve as a result of strength training.
And – as in the first piece of work – the strength training had a greater impact on cycling than on running. Total cycling time @ 80 per cent max ballooned about 20 per cent (from 71 to 85 minutes) after the 10 weeks of strength training, but average 10-K times improved to a much smaller extent (less than 2 per cent) – from 42:27 to 41:43. In fact, this improvement in 10-K running capacity, although real, was not quite statistically significant.
Somewhat surprisingly, short-term endurance (running or cycling for as long as possible at about VO2max), increased by approximately the same amount (12 per cent) for both cycling and running (from 362 up to 403 seconds while cycling and from 361 to 407 seconds for running). The only logical conclusions to draw from these results are that strength training can boost the performances of experienced runners and cyclists, and that a key factor in this improvement is enhanced economy (since VO2max and lactate threshold did not get better, economy is the only major physiological variable left).
To summarize, Hickson’s two studies showed that strength training could directly boost running performance, especially during exertions carried out at high intensities over fairly short periods of time, in both experienced and inexperienced runners. The pair of investigations also provided indirect evidence that strength training could improve running economy.
Swedish scientists check in
It was left for a third study, carried out in Scandinavia, to strongly verify the link between strength training and economy (remember that although Hickson’s studies had suggested that strength training improved efficiency, economy wasn’t directly measured). This third piece of research happened to use the most specific form of strength training for runners – hill running (we like to call hill running a strength workout rather than a standard running session because hill running involves working against resistance (gravity) and lifting a weight (body mass) from a lower to higher point (from the bottom to top of the hill). The beauty of hill work is that it is completely specific to running, and the number of ‘reps’ are tremendous (during hill efforts, a ‘rep’ is simply an upward push of the body by one leg, so there are about 180 ‘reps’ per minute, assuming that a runner is ascending with a stride rate of 90).
Carried out by Jan Svedenhag and Bertil Sjodin, two exercise physiologists at the Karolinska Institute in Stockholm, Sweden, the hill-economy study involved 11 Swedish marathon runners who added hill workouts to their training for a 12-week period (‘Endurance Conditioning,’ in Endurance in Sport, R. J. Shephard and P. O. Astrand, Eds., Blackwell Scientific Publications, pp. 294-295, 1992).
The Swedes used fairly steep, 400-metre hills for their strengthening work, and employed a variety of intensities – from relaxed, easy striding to very hard efforts. However, a unique feature of the training was that the Swedes employed ‘bounce’ running for many of their ascents. In bounce running, the idea is not to lean forward and charge up the hill as quickly as possible; instead, each step involves a dramatic, vertical spring. For example, after your right foot makes contact with the hill, you spring upward using close-to-maximal contractions of the muscles in your right leg and propelling your left knee as high as possible as you become airborne. You then land on the front part of the left foot and let the left heel sink quickly down below the level of your toes, before springing vertically again while raising the right knee as high as possible. You are basically moving up the hill with a series of exaggerated vertical leaps. Even though each leap is rather impressive, actual progress up the hill proceeds at a fairly moderate pace.
After 12 weeks of this varied hill running (carried out a couple of times per week), the Swedes improved their running economy by about 3 per cent, which would shave about four minutes from a 2:12 marathoner’s finishing time – without any feeling of increased effort. Interestingly enough, the gains in economy were greatest at relatively modest (6:30 per mile) paces – and very small at fast (4:50 per mile or faster) running velocities. That shouldn’t be a surprise, though: remember that hill running on any kind of significant incline tends to be somewhat slow running (after all, the hill slows you down), especially if you’re spending your time ‘bouncing’ up the slope. That’s why you have to combine (or follow up) your hill training with some high-speed bounding and running, so that you can also be more economical at race-type velocities, and so that you can combine the strength and economy gained from the hills with the improved coordination and quickness accruing from the quicksilver training – and thus become a truly more powerful runner.
Alternating the heavy and the light
To use a baseball analogy, pitchers who train with heavy balls and light balls always end up throwing more powerfully than those who use only regular balls. Working with a heavy ball slows down arm- and shoulder-movement speed, just as running up hills slows striding rate, but it increases total muscular force production (to overcome the greater resistance provided by the heavier ball), just as running uphill makes leg muscles create greater force As a result, muscles are forced to improve their basic strength.
However, that says nothing about actual power (the rate at which this strength is applied, eg, the throwing velocity of a pitcher or the running speed of a runner). After all, you can be considerably stronger, but still be as slow as molasses. If you want major gains in power, you’ve got to combine your basic strengthening work with high-speed stuff. For baseball pitchers, this means throwing with the lighter ball. Since the gossamer ball provides less resistance, the shoulder and arm move much more quickly, and the nervous system learns to control and coordinate such lightning-quick activity. For runners, the quest for power means following up your strengthening with some tearing along at higher-than-usual speeds, so that the nervous system learns to synergize very rapid muscular contractions. Put the two together – brute strength and highly coordinated quickness – and you have a pitcher with ‘hop’ on his fastball or a runner who is setting some new PBs.
Summarizing the Swedes’ study, we can say that specific strength training for runners (e. g., hill running) definitely improves economy. However, that economy enhancement may be present only at relatively modest paces, if the majority of hill running occurs at medium speed. For broader economy improvement and for real upstrokes in power, it’s undoubtedly necessary to combine hill running with some sizzling sessions on the track.
A final piece of evidence
One final study provides convincing evidence that strength training can boost economy in runners. In this most-recent piece of research, which was carried out at the University of New Hampshire, six experienced female distance runners added upper- and lower-body strength workouts to their regular running program during a 10-week training period, while six other female runners did no resistance training and continued their usual running for 10 weeks. The women, who ran four to five days a week for a total of 20-30 weekly miles, were in 38:30 to 45:00 10-K shape. None of the athletes had engaged in strength training during the three-month period which preceded the study (‘Strength Training in Female Distance Runners: Impact on Running Economy,’ Journal of Strength and Conditioning Research, vol. 11(4), pp. 224-229, 1997).
The strength-trained group carried out resistance training on Monday, Wednesday, and Friday each week. There were two different strength sessions: ‘Strength workout A’ consisted of parallel squats*, knee flexions, straight-leg heel raises, seated presses*, rear-lat pulldowns, hammer curls*, and weighted sit-ups*. ‘Strength workout B’ was composed of lunges*, knee extensions, bent-leg heel raises*, bench presses*, seated rows, front-lat pulldowns, and abdominal curls (exercises with an asterisk were performed with free weights). The strength-trained group conducted workout A on Monday, workout B on Wednesday, session A on Friday, workout B on the following Monday, and so on throughout the 10-week period, alternating session A with session B throughout the full 70-day programme. When running and resistance training took place on the same day, the running workouts and strength-building sessions were always separated by at least five hours of rest.
The actual number of sets and reps in the strength workouts were as follows:
Workout A Weighted sit-ups: 2 x 15 (2 x 15 means two sets of 15 reps) Straight-leg heel raises: 2 x 12 Knee flexions: 3 x 8 Rear-lat pulldowns: 3 x 8 Parallel squats: 3 x 6 Seated presses: 3 x 6 Hammer curls: 3 x 6
Workout B Lunges: 3 x 6 Bench presses: 3 x 6 Knee extensions: 3 x 8 Seated rows: 3 x 8 Front-lat pulldowns: 3 x 8 Bent-leg heel raises: 2 x 20 Abdominal curls: 2 x as many as possible.
Two-minute rest intervals followed each set, and in all cases the resistance was adjusted so that complete fatigue was reached after the indicated number of reps (no further reps could be completed during a set). Most of the exercises are familiar ones; the only exception might be ‘hammer curls,’ which are just biceps curls carried out with the palms of the hands facing toward the body, instead of facing straight ahead.
After 10 weeks, the strength-trained runners improved their upper-body strength by 24 per cent and raised their lower-body strength by 34 per cent, while the non-strength-trained athletes failed to boost muscle strength at all. In addition, there was a trend for exercise heart rate to diminish in the strength-trained group. Before strength training, the women ran with a heart rate of 187 beats per minute while cruising at 6:30 per mile pace; after strength training, their pulse rate registered 183 at the same running tempo. Likewise, heart rate at seven-minute tempo dropped from 181 to 177 beats per minute. Most significantly, running economy also improved in the strength-trained group – but didn’t change at all in the runners who did no strength training.
In fact, at the end of the study, it ‘cost’ the strength-trained runners about 4 per cent less oxygen to run at their original 10-K race pace of approximately 6:30 per mile. This means that after strength training the runners could complete their 10Ks much more easily – or better yet – that they could run their 10K races at a pace of 6:17 per mile without experiencing any feelings of increased effort! That positive change would produce more than an 80-second improvement in 10-K time. Indeed, those strength-trained runners who actually raced at the end of the 10-week period reported improvements at race distances from 5K to the half marathon.
The strength increases and economy enhancements in the strength-trained runners were not accompanied by upswings in body mass or body-circumference measurements. In other words, the strength-trained runners did not ‘bulk up’. You may be reassured by that, since many runners don’t relish the idea of having bulkier thighs or carrying around extra weight as they run.
Why does such basic strength training improve running economy? As we’ve mentioned, resistance training enhances the strength of individual muscle cells in runners’ leg muscles. With more strength per cell, fewer fibres needed to be activated during running, lowering the total oxygen demands of the leg muscles.
Second, as New Hampshire researcher Ron Johnston points out, ‘Excessive, unnecessary body motions during running waste energy and use up oxygen. As the resistance-trained runners in Johnston’s study became stronger, their body parts became more stable during running. Since there was less unnecessary motion, the total oxygen demand decreased.’
Third, strength training, if it is specific to running, improves the coordination of muscle activity by the nervous system, allowing more propulsive, forward force to be exerted for every calorie of energy consumed (and for each quantity of oxygen gobbled up by the muscles). The great news is that the improved running economy which results from strength training leads to more trouble-free workouts and better race performances.
So what’s the bottom line? Many runners just run to work out, avoiding resistance training like the plague. That’s a bad idea, because strength training can enhance economy and trim time from race efforts. However, strength training shouldn’t be conducted haphazardly: you need to progress intelligently in your strength work from fairly easy to difficult efforts – and from work which provides general strength upgrades to exertions which specifically boost strength and power while running. In short, your strength training needs to be periodized properly.