The following is a post on research and training recommendations from the now-defunct website Running Research News which was run in the early 2000s by Owen Andreson, author of the excellent book Running Science.
Another excellent book from Anderson is Running Form.
Anderson has contributed so much valuable information on training to the distance running community. I personally am indebted to him and share his archive work so more can learn from him.
Plyometrics and Distance Running
By Owen Anderson, Ph. D.
Evidence that plyometric training improves running economy and distance-running performance continues to pile up. In recent research carried out by Rob Spurrs and colleagues from the Human Movement Department at the University of Technology in Sydney, Australia, just six weeks of plyometric work (with 15 total plyometric sessions) improved 3-K run time by almost 3%!
17 male distance runners with an average age of 25 who had been actively training for approximately 10 years participated in the Australian investigation; nine were assigned to a control group, and eight took part in the experimental, plyometric training (1). Prior to the study, all 17 athletes had an average weekly training volume of 60 to 80 kilometers (37 to 50 miles). None of the subjects had performed plyometric exercises during the three months leading up to the study.
Runners in the experimental group completed two plyometric workouts per week for three weeks and then three plyometric sessions each week during the final three weeks of the study. Prior to each plyometric session, all of the runners carried out a 20-minute, dynamic warm-up which included leg swings, ankle bounces, skips, and run-throughs; some static stretching was also performed. The plyometric training was designed to be progressive, in the sense that the exercises became more complex, more sets of drills were completed, and the total number of foot contacts per session increased during the six-week period. The plyometric drills included squat jumps, split-scissor jumps, double-leg bounds, alternate-leg bounds, single-leg forward hops, depth jumps, double-leg hurdle jumps, and single-leg hurdle hops. For all of the exercises, the runners were instructed to give maximal efforts with minimal ground-contact times.
The pervading theme for all of the exercises used in the investigation was to get as high as possible with the least amount of ground-contact time. For the double- and alternate-leg bounds and also for the single-leg forward hop (i. e., the drills which focused more intently on horizontal movements), this theme was also applied - but with the added instruction that the greatest-possible horizontal distance should be covered with the most-abbreviated-possible ground contact.
After the six weeks of explosive training, average 3-K performance improved by 16.6 seconds (2.7%) in the plyometric group, dropping from approximately 10:28 to 10:12; meanwhile, control-group runners failed to improve 3-K times. Plyometrically trained runners also upgraded their "five-bound" test distance by 7.8% and countermovement jump height by a sizable 13.2%. The five-bound test called for the runners to cover the greatest horizontal distance possible by performing a series of five forward jumps with alternate left and right foot contacts. The countermovement jump test involved three countermovement jumps on a Swift Performance Jump Mat (countermovement jumps include a significant squatting action prior to jumping). For these countermovement jumps, the runners attempted to jump for maximal height while keeping their hands placed on their hips (to reduce potential propulsive contributions from the upper body). The best of the three jumps was recorded for analysis. Improvement in both the five-bound and countermovement tests indicated that the plyometric runners had significantly improved maximal force production in their leg muscles and/or coordination during intense movements. Control runners failed to improve on either test.
The plyometric group also made significant improvements in another key area - running economy.
Economy, which is simply the rate of oxygen consumption required to run at specific rate of movement, was checked at three different running speeds, and the plyometrically trained runners improved economy at all three velocities. Their economy was 6.7-% better at 12 kilometers per hour, 6.4-% improved at 14 kilometers per hour, and 4.1-% more up-to-date at 16 kilometers/hour, compared with the beginning of the six-week study. Control runners failed to improve economy at all!
Making plyometric training look better still, maximal isometric force in the calf muscles of the plyometric runners swelled by 11 to 14% over the course of the six-week investigation, and the rate of force production by the calf muscles showed strong positive trends in the plyometric athletes, advancing by about 14 to 15%. Control runners failed to show any signs of improvement.
Quite rightly, the Australian researchers took a keen interest in the musculotendinous stiffness (MTS) of the runners before and after training.
As it turns out, the link between MTS and performance has a very interesting history. About 12 years ago (1991), research revealed that the MTS of the legs determined the body's ability to store and utilize impact energy associated with running (2). Subsequent research found that seven weeks of plyometric training led to a significant increase in leg-tendon stiffness (3). Even more interestingly, other research determined that the actual energy cost of running was significantly related to the stiffness of the legs during propulsion - and that when such stiffness decreased, the energetic cost of running actually increased (4). In a similar vein, additional research suggested strongly that uneconomical runners possess a more compliant running style during ground contact, compared with energy-efficient harriers (5).
If this is a puzzler to you, bear in mind that a stiff muscle or tendon tends to resist being stretched out, but it also develops a comparatively high degree of tension as it is elongated, compared with a non-stiff muscle or tendon. Stretch a stiff muscle/tendon out three centimeters, for example, and it will snap back like an angry cobra when allowed to do so; stretch a non-stiff muscle/tendon out the same distance, and it will recoil rather limply.
Naturally, the key muscles and tendons of running, including the calf muscles, Achilles tendon, quadriceps muscles, patellar tendon, glutes, and hamstrings, all are stretched significantly when the foot makes impact with the ground. If these muscles and tendons are too non-stiff, the leg collapses to too great an extent; if the tissues are stiffened up, the leg is better able to produce optimal amounts of reactive, propulsive force. In effect, the impact energy of running is stored and released more effectively. This should improve economy, since very forceful, non-energy-requiring "snap-backs" of muscles and tendons are being used to furnish a significant amount of the energy needed to drive the body forward; there is a lesser reliance on energy-consuming muscle contractions.
So how did the plyometric runners fare with their stiffness? How about a nifty 11-% average upswing in stiffness for the right leg and a 15-% vault upward for the left limb? Meanwhile, the hapless control runners failed to augment leg stiffness at all. Remember that running economy also improved by 4 to 7% in the plyometric runners - and by 0% in the control competitors. It is logical to think that one of the key things plyometric training can do for runners is help them assess how much stiffness is required in their legs to produce the most highly propulsive and most highly energy-efficient muscle-tendon actions.
Rob Spurrs' excellent work echoes research carried out a few years ago by Heikki Rusko and co-workers in Finland. In Heikki's heroics, 10 runners spent 32% of their training time (that is, about three hours per week) carrying out explosive strength training (6). The explosive sessions lasted from 15 to 90 minutes and consisted of sprints (five to 10 reps of 20 to 100 meters) and various jumping exercises (bounding drills, bilateral-countermovement jumps, drop-and-hurdle jumps, and one-leg-five-jump tests). Sometimes, these jumps were carried out without additional weight; at other times a barbell was held on the shoulders. In addition, these "explosive" athletes completed leg-press, knee-extensor, and knee-flexor exercises with low resistance and close-to-maximal movement velocities (five to 20 reps per set, 30 to 200 total reps per session, with resistance always at less than 40% of the one-rep maximum). A control group spent only 3% of total training time performing such exercises but logged more weekly mileage than the explosive athletes (about 70 miles per week, versus 45).
After nine weeks, contact time (the amount of time spent on the ground by the feet during the stance phase of the gait cycle) decreased from 210 milliseconds to 195 milliseconds for the explosively trained runners, while the control people remained unchanged. Happily, stride length remained unaltered in the explosive group (naturally, there is a tendency for stride length to shorten as contact time is abridged), which meant that the explosive runners were faster (after all, isn't that what explosive runners are supposed to be?). Running economy improved by 8% in Heikki's explosive competitors (just above, but not necessarily significantly so, the 4- to 7-% gain achieved by Robb's runners). Heikki's control runners got an "F" for economy enhancement, despite their valiant, 70-mile per week efforts.
Rusko's explosive runners augmented 20-meter sprint times by 4% and - most importantly (since they were 5-K runners) - shaved 30 seconds off their 5-K race times, while control-runners' times were stagnant. Incredibly, Rusko's explosive individuals accomplished their 5-K feats even though they made no improvement at all in maximal aerobic capacity (VO2max). Meanwhile, control runners were upticking VO2max by 5% but failed to ameliorate 5-K time by even one second!
Rob Spurrs, the principal researcher in the Australian work, is an excellent runner in his own right, having clicked off 800 meters in 1:49.6 and - even more impressively - 400 meters in a sizzling 48.7. He is currently the rehabilitation conditioner for the Sydney Swans, an Australian-Rules Football Club, and is undertaking new research which will measure peak braking force, time to peak braking force, average braking force, peak propulsive force, time to peak propulsive force, average propulsive force, peak vertical force, vertical force, time to peak vertical force, average vertical force, and contact time in explosively trained and non-explosively trained runners. He will also be videotaping runners in both groups in order to monitor changes in kinematics, especially with regard to flight and contact times.
Interviewed by Running Research News for this article, Spurrs said, "Regarding the theory of increased muscle-tendon stiffness leading to improved economy - and I say this prior to our new testing taking place - I believe that with a stiffer system, the athlete will gain greater forward propulsion with each foot strike at an energy cost which is less than before. Thus, for a specific speed, increased stiffness will lead to greater economy."
And there you have it! The bottom line is that explosive strength training leads to improvements in performance which seem to be related to higher rates of force production and enhanced economy while running. Robb's study detected a 2.7-% upgrade in 3-K times, while Heikki's investigations noted a 2.7-% (!) enhancement of 5-K ability.
References
(1) "The Effect of Plyometric Training on Distance Running Performance," European Journal of Applied Physiology, Vol. 89, pp. 1-7, 2003
(2) "Optimal Stiffness of Series Elastic Component in a Stretch-Shorten Cycle Activity," Journal of Applied Physiology, Vol. 70, pp. 825-833, 1991
(3) "Influence of Plyometric Training on the Mechanical Impedance of the Human Ankle Joint," European Journal of Applied Physiology, Vol. 76, pp. 282-288, 1997
(4) "The Spring-Mass Model and the Energy Cost of Treadmill Running," European Journal of Applied Physiology, Vol. 77, pp. 257-263, 1998
(5) "Leg Spring Characteristics and the Aerobic Demand of Running," Medicine and Science in Sport and Exercise, Vol. 30, pp. 750-754, 1998
(6) "Explosive Strength Training Improves 5-Km Running Time by Improving Running Economy and Muscle Power," Journal of Applied Physiology, Vol. 86(5), pp. 1527-1533, 1999
