Posted: April 8, 2005

Science of Sport: Swedish-Cured Ham Is Right Recipe For Rejuvenated Running

By Owen Anderson, Ph. D. (copyright © 2003-2005)

Hamstring strains and injuries are common occurrences in both distance and sprint running, and exercise scientists have searched for ways to minimize the risk of hamstring problems during training and competition. Since deficiency in hamstring strength has been cited as a key risk factor for hamstring injury (1), many researchers have suggested that appropriate strengthening of the hamstring muscles would ease the risk of trouble (2). Studies carried out with animals certainly support this idea; such research clearly demonstrates that a stronger muscle can absorb more force prior to failure, compared with a weaker muscle (3). However, until now no prospective study has actually taken a look at whether a hamstring-strengthening regime would actually lower the hurt in hamstrings during an extended period of training or a competitive season.

That deficiency has now been corrected, thanks to great research carried out by the affable Carl Askling and his co-workers at the famed Karolinska Institute in Stockholm and Sahlgrenska University Hospital in Goteborg, Sweden. In this new study, 30 male soccer players from two of the best premier-league teams in Sweden participated; goalkeepers, injured players, and athletes with chronic hamstring troubles were excluded (4). The players were randomly assigned to either a hamstring-training or control group, and there were no significant differences between these groups with respect to age, body mass, height, body-mass index, muscle strength, maximal running speed, or hip flexibility (range of motion) when the study began.

In the hamstring group, special hamstring training was carried out over a 10-week period prior to the beginning of the competitive season. 16 sessions were competed during the 10-week time frame - every fifth day for the first four weeks and every fourth day during the last six weeks. A 15-minute warm-up of jogging or cycling preceded each workout.

The actual hamstring training concocted by Askling and his crew included both concentric and eccentric actions and was carried out on a YoYo™ flywheel ergometer. This ergometer is a relatively new training device (5) which requires an athlete to use concentric muscle actions to start a flywheel into rotational motion – and then to utilize eccentric muscle actions to decelerate the rapid, reverse rotational movement of the flywheel. As a unique feature of the YoYo™ ergometer, eccentric overload of muscles is accomplished, i. e., extra force must be generated by the sinews as they are stretched out with each attempt to control the quick motion of the flywheel.

The YoYo™ device was co-invented by two impressive Swedish researchers, Hans Berg, Ph. D. and Per Tesch, Ph. D. Berg is an alpine skier and Tesch a flat-water kayaker, and both have an extensive research background and have worked with professional and amateur athletes, helping them improve their strength and power. In the 1990s, Tesch carried out investigations at NASA’s Kennedy Space Center, the goal of which was to maintain astronauts’ muscle mass and strength during space flight. Collaborating with Berg, Tesch subsequently developed the YoYo™ trainer as a device which could provide outstanding resistance training in a zero-gravity environment; YoYo™ machines are scheduled to leave earth on European-Space-Agency rockets (with astronauts on board, too, of course) in the next year or so. It did not escape the attention of the Swedes that YoYo™ equipment could be utilized successfully on earth, too, and YoYo™ leg-curl, leg-extension, calf-raise, and abdominal-crunch machines are now available on the commercial market. For further information, take a look at http://www.yoyotechnology.com, or telephone Jay Trieschmann at Dynamic Training Systems, Inc. here in the United States (501-993-2961). There is no affiliation between Dynamic Training Systems and Running Research News or SSS Publishing, Inc.

The specific details of Carl Askling’s training program were as follows: The athletes performed bilateral knee-flexion actions from a prone position on the YoYo™ ergometer, accelerating the flywheel by concentric action of their hamstrings – and then decelerating it with eccentric action of their hammies (please see the picture of Ludmilla Enquist to get a better feeling for the movements). The athletes had to apply maximal effort from a straight-leg position until almost full knee flexion was attained (130-140 degrees); on the “way back down,” the athletes attempted to brake the flywheel movement once the 90-degree position was reached. Braking continued with maximal effort until the knees were straight again, completing one rep. Each training session consisted of four sets of eight reps, with a one-minute recovery between sets.

There are several good reasons why Askling chose to emphasize eccentric strengthening of the hamstrings in this pre-season training. First, research has shown that eccentric training may produce more dramatic strength gains than concentric training (6 & 7). Second, athletes with a history of hamstring injury have been linked with “eccentric peak torque deficits” in their hamstrings, suggesting that an inability of the hamstrings to produce generous amounts of power during eccentric actions may predispose the tissue to injury (8). In theory, correcting these eccentric deficits should decrease the risk of getting hurt.

In addition, it is now commonly believed that damage to the hamstrings during running usually occurs during the eccentric phase of hamstring action when the hamstrings are working to control the forward swing of the leg. As each leg swings forward during the gait cycle, the hamstrings in the relevant leg attempt to contract to limit the forward movement but are actually elongated as the leg moves forward, putting the hams under a state of high tension. In this scenario, the hamstrings may either be harmed during very high-speed running, when the ripping-apart forces on the hamstrings are very high, or during extended, submaximal running, when the hamstrings may become fatigued and less able to absorb the repeated forward force. For example, in a three-hour marathon, the hamstrings in each leg are forced to work eccentrically to control forward swing more than 16,000 times. It is small wonder that we see many marathoners clutching their hams at the 22-mile mark (or thereabouts) in the race – or nursing their hamstrings for several days after completion of the event. Thus, the focus on eccentric hamstring action in Askling’s study was an attempt to strengthen the hams during the movement which is potentially most damaging to them.

After the 10-week training period, eccentric knee-flexor strength vaulted upward by 19 percent and concentric knee-flexor strength improved by 15 percent in the hamstring group, whereas there were no improvements at all in the control subjects. Interestingly enough, maximal running speed was also enhanced in the hamstring group but did not budge for the control athletes. Maximal running speed was measured during a “flying” 30-meter sprint after a 20-meter acceleration on an indoor track, and the ham group became swifter by 2.4 percent (from 3.36 to 3.28 seconds) after the 10 weeks of hamstring training; control-group athletes remained stagnant at precisely 3.38 seconds.

During the competitive season which followed the 10-week training period, 13 hamstring injuries occurred among the 30 players, but only three of these maladies were observed in the hamstring-trained group (20 percent), with 10 mishaps (67 percent) delegated to the control subjects; this difference was statistically significant.

The bottom lines? Carl Askling’s special pre-season hamstring training with a special focus on eccentric work for the ‘strings not only lowered hamstring injury rate in the subsequent competitive season; it also boosted maximal running speed. It is reasonable to expect that both sprint and endurance runners might enjoy similar benefits from appropriate hamstring fortifying.

Why exactly was the hamstring injury rate lower after the special training? It is likely that the improved eccentric strength of the hams resulting from the training made the athletes’ hamstrings more resistant to serious strain during training and competition. How could the Swedish hamstring exertions, carried out in a prone body position with isolated, open-kinetic-chain actions, actually make the athletes faster? The extra stress placed on the hamstrings by the YoYo™ ergometer evidently increased the hamstrings’ force capacities in a general way, so that when specific soccer training combining speed and skilled movement was carried out, the increase in capacity was carried over to the integrated motion of running.

If you are not ready to bounce up and buy a YoYo™ ergometer just yet (the cost of a single leg-curl unit is $2850), bear in mind that concentric-eccentric action can be achieved with the hamstrings while lying prone on a bench (with weight attached to the ankles or a dumbbell held between the ankles). The movement, commenced with straight legs extended from the end of the bench (your kneecaps should be just off the end of the bench), would involve flexing the knees to 90 degrees (so that the soles of your shoes are facing the ceiling) – and then tightly controlling (in an eccentric manner for the hams) the downward movement of the weight as the legs are straightened again. A training partner could help you add weight for the eccentric portion of the overall exercise.

Another great eccentric exercise for the hamstrings is called kneeling hamstrings. To perform this one, kneel on a comfortable surface, with your torso upright and your feet held in place by a partner. Then, lean forward with your whole body from the knees, while keeping the portion of your body from your knees to your head in a straight line. Return to the initial kneeling position to complete one rep. This exercise is usually performed without weights (although you may wear a weight vest, hold a weight at your chest, or place a bar on your upper back once you have become proficient), but it is extremely challenging to the hamstring muscles of many runners. It is best to start with fairly small movements and – as always - to carry out a nice warm-up ahead of time.

Finally, the most running-specific, eccentric hamstring strengthener would have to be bicycle leg swings. To do these, stand with your weight fully supported on your left leg (initially, you may place your right hand on a wall or other support to maintain balance). Begin by flexing your right hip and raising your right knee up to waist height (your right thigh should be parallel with the ground); as you do this, your right knee should be flexed to 90 degrees or more. Once your thigh is parallel to the ground, begin to extend your right knee (swing the lower part of your right leg forward, unflexing the knee) until your knee is nearly fully extended (your leg is nearly straight), with your right thigh still parallel to the ground. As your right knee nears full extension, allow your right thigh to drop downwards and backwards until the entire thigh and leg are extended behind your body (as if you were following through on a running stride). Your right knee should be near full extension (your leg should be basically straight) until it reaches the peak of the backswing. As your right hip nears full extension (as you approach the end of the backswing), raise your right heel by bending your right knee; your heel should move closely towards your buttocks as you do this. As this happens, move your right knee forward until it returns to the appropriate position in front of your body, with your right thigh parallel to the ground. Repeat this entire sequence of actions in a smooth manner such that the hip and leg move through a continuous arc without stopping or pausing.

Once you are able to coordinate the movement, strive to perform the swings at a cadence of about 12 swings every 10 seconds or so (slightly faster than one swing per second). When you feel comfortable carrying out the basic routine, purchase an intermediate-strength “stretch cord” from a reliable supplier such as the M-F Athletic Company (http://www.performbetter.com), and complete the exercise while utilizing the stretch cord, which should be attached to your “swing” (non-support) ankle at one end and a firm post, table leg, fence, railing, or other structure (at roughly knee height) at the other end (there is no affiliation between M-F and Running Research News or SSS Publishing, Inc.). Stand facing the post, table leg, fence, or railing, with enough distance between you and the structure so that the stretch cord significantly accelerates your leg forward during the forward-swing phase of the exercise. This enhanced forward acceleration will put your hamstrings under additional stress – and will ultimately be very strengthening for your hams. 50 reps per leg are greater for starters, and you can progress to three sets of 50 repetitions while boosting your speed and advancing to a higher-resistance stretch cord. ©

References

(1) “Factors Associated with Hamstring Injuries,” Sports Medicine, Vol. 17, pp. 338-345, 1994
(2) “Hamstring Injuries in Sprinting – The Role of Eccentric Exercise,” Journal of Orthopaedic and Sports Physical Therapy, Vol. 10, pp. 343-349, 1989
(3) “Muscle Strain Injuries,” American Journal of Sports Medicine, Vol. 24, pp. 2-8, 1996
(4) “Hamstring Injury Occurrence in Elite Soccer Players after Preseason Strength Training with Eccentric Overload,” Scandinavian Journal of Medicine and Science in Sports, Vol. 13, pp. 244-250, 2003
(5) “A Non-Gravity Dependent Ergometer to Be Used for Resistance Training in Space,” Aviation, Space, and Environmental Medicine, Vol. 65, pp. 752-756, 1994
(6) “Adaptive Responses to Muscle Lengthening and Shortening in Humans,” Journal of Applied Physiology, Vol. 80, pp. 765-772, 1996
(7) “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
(8) “Hamstring Muscle Strain Recurrence and Strength Performance Disorders,” The American Journal of Sports Medicine, Vol. 30(2), pp. 199-203, 2002

To learn about Owen-Anderson's running camps in California, please send a note to Owen at owen@rrnews.com.

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