Is Resisted Sprint Training Effective?

Coaches in sports requiring  high acceleration and all-out sprint speed have increasingly endorsed sprint training resisted by a variety of means including weighted vests, towed weighted sleds, long elastic cords, or straps for towing another individual. Yet there have been few studies examining the effectiveness of such training. A recent study by Clark et al. in the Journal of Strength and Conditioning Research evaluated the effectiveness of two types of resisted sprint training.

Experimental Procedure
There were 3 groups of  collegiate lacrosse players that trained twice a week for 7 weeks as follows:

• Weighted Sled: 7 of the subjects trained while towing 10% of their bodyweight in a sled
• Weighted Vest: 6 of the subjects wore vests containing 18.5% of their bodyweight
• Unresisted: 7 of the subjects did not use any resistance device during their training

For all groups, each training session consisted of 7-10 sprint intervals of 20-60 yards (18.3-54.9 m) separated by rest intervals of 3-4 minutes. Both before and after training, all subjects were tested as to their sprint-speed over 40 yards (36.6 m) after a 20-yard (18.3 m) running start.

Results
For the subjects as a whole, there was significant reduction (-1.1%) in the time taken to sprint 40-yards. However, there was no significant difference in improvement between any of the training groups. However, the percentage of improvement of the unresisted training group (-2.0%) was greater than for the weighted sled group (-0.1%) or the weighted vest group (-1.2%).

Bottom Line
The fact that the number of subjects in each group was relatively low made it difficult to obtain statistically significant differences in improvement between groups. However, it does appear that the resisted training was no more effective than unresisted training for improving 40-yard sprint speed following a running start. Because the timed portion of the sprints followed a running start in this study, the results do not address the effectiveness of resisted sprint training for improving the initial acceleration phase of a sprint.

Estimating the Caloric Cost of Running or Walking

A recently published article by Loftin et al. in the Journal of Strength and Conditioning Research (vol. 24, no. 10, pp. 2794-2798, 2010) measured the caloric consumption per mile of 19 normal-weight walkers, 11 overweight walkers, and 20 marathon runners. The subjects were about evenly divided among males and females.

Results

• Caloric consumption was more related to lean body mass than to total body mass
• Men burned more calories per mile than women
• Men and women did not differ in calories consumed per mile per unit body mass
• In terms of calories per mile per unit body mass, marathon runners burned significantly more than normal-weight walkers who burned significantly more than overweight walkers

The following equation was developed from the experimental data to predict an individual’s caloric consumption per mile:

Men weighed in kilograms:

Calories per mile = (0.789 x kg body mass) + 43.5

Men weighed in pounds:
Calories per mile = (0.3586 x lb body mass) + 43.5

Women weighed in kilograms:

Calories per mile = (0.789 x kg body mass) + 35.8

Women weighed in pounds:
Calories per mile = (0.3586 x lb body mass) + 35.8

Bottom Line

The equation can be useful for those interested in estimating the caloric cost of their walking or running workout.

Minimalist or “Barefoot” Running Shoes

For decades, running shoes were rated by Runner’s World magazine and other organizations largely on their ability to absorb shock. As a result, manufactures made heels and soles increasingly thick to rank highly in the ratings. This led to shoes that were quite bulky and thickly padded. In a countermovement to this trend, and inspired by a track coach who included barefoot running is his training programs, Nike came out with the first of the modern minimalist shoes, the Free, in 2004. This lightly-padded shoe was only intended for occasional use, not full weekly mileage.

Proponents of minimalist running shoes say that, because of their light cushioning, people running in them alter their gait to lessen shock. Such changes include landing on the midfoot or forefoot rather than the heel, shortening the stride, increasing stride frequency, and lowering peak impact force. This is claimed to reduce this risk of tibial stress fracture, plantar fasciitis, and other overuse injuries, and to strengthen the feet. Biomechanical testing has verified that Africans who grow up running barefoot strike the ground with only a third of the impact experienced by U.S. runners in shoes. Lightweight shoes also lower the energy cost of running, so a runner can go at a faster pace at the same level of exertion, which translates into faster race times.  However, running experts have cautioned that any switch from heavily cushioned standard running shoes to minimalist shoes must be gradual in order to allow the muscles, bones, and tendons of the foot and leg to adapt.

The minimalist running shoe movement accelerated significantly with the publication of the 2009 book, “Born to Run,” which revealed that the Tarahumara Indians of northern Mexico get fewer injuries than U.S. runners even though they wear very thin rubber sandals and run extremely long distances. Manufacturers other than Nike came up with their own versions of minimalist shoes. Vibram, an Italian company, introduced its Five Fingers model, in which each toe is individually gloved. It weighs a scant 5.7 oz and has a heel thickness of only 7.2 mm (compared with up to 38 mm on heavily padded “cushion” or “motion control” shoes). This model is now the leader of the minimalist shoe market.

Other running shoe companies have jumped on the minimalist bandwagon. Saucony came out with its Kinvara model, which has somewhat more protection than the free and is intended for regular, rather than occasional, use. New Balance will debut its Minimus in February, which the company says will give a free-foot feel but still have cushioning in key spots. Merrel will put out its Barefoot Collection in February with a sole from Vibram and a very light upper. Also in February, Nike will supplement it Free line with its Lunar Eclipse lightweight stability trainer. Addidas will introduce a light, fast, everyday shoe in the Fall of 2011. Other companies that do not plan to introduce minimalist shoes have been making their existing models lighter and more flexible. Yet there is concern within some shoe companies that runners may switch to minimalist shoes too rapidly and subject themselves to injury.

An important factor in how long it takes to adapt to a minimalist shoe is the difference in thickness between the forefoot and heel padding. It can range from zero for a shoe with no difference between the thickness of heel and forefoot padding, to a 12 mm greater thickness of heel than forefoot padding. If one has been accustomed to running in a heavily padded shoe with a large difference between the padding thickness of heel and forefoot, the adaptation time to a minimalist shoe should be considerable.

As of now, there have been no published articles comparing the injury rate of runners wearing minimalist shoes vs. those training in standard shoes. However, many of the runners who have switched to minimalist shoes swear by them. Yet few market watchers expect such shoes to ever capture a major share of the running shoe market. Currently, no more than 10% of running shoes sold could be called minimalist.

Bottom Line
While few studies have been done on minimalist shoes, evidence suggests that such shoes do alter running gait so as to reduce the degree of foot-strike impact and also allow the foot to flex in a natural manner while in contact with the ground. However, since most Americans have grown up walking, running, and playing sports  in supportive shoes with heels more thickly padded than forefeet, the adaptation to relatively flat and lightly padded shoes can be difficult and potentially injurious. Additionally, such shoes offer little protection against foot injury that can occur when stepping on a rock, tack, or other object. Those who are willing to accept the risk of trying such shoes should do so with caution and increase the weekly mileage they run in them very gradually. It remains to be seen whether the benefits of minimalist shoes outweigh their risks.

Static Stretching Can Impair Distance Running Performance

At times it can be difficult to find sports science articles that have true relevance to athletes. But here's one that can have real impact. A study by Wilson et al. (Journal of Strength and Conditioning Research, vol 24, no. 9, pp. 2274-2279, 2010) provides strong evidence that static stretching before a distance-running event can impair performance among young, male athletes.

Static stretching involves stretching a muscle to the point of mild discomfort and holding the stretch for 10-30 seconds. We have previously highlighted previous evidence that static stretching can impair jumping performance. It has also been shown to reduce maximal leg-press strength, 20-meter sprint speed, and knee-extension torque. Yet this is the first study to examine the effect of static stretching on endurance performance.

Experimental Procedure
10 male collegiate competitive distance-runners and triathletes who ran at least 20 miles per week and were in excellent aerobic condition were tested on 2 different days, at least a week apart, after the following:

1. 16 minutes of stretching consisting of the following 5 stretches each performed 4 times for 30 seconds of holding:: 1) sit on floor with knees straight and reach with both hands to and beyond the toes, 2) stand with balls of feet on a block, letting bodyweight stretch calves, 3) for both left and right, stand on 1 leg and pull the opposite heel toward the butt 4) for both left and right, lunge deeply, and 5) cross the left leg over the right one, and pull the right thigh towards the torso, repeating for other side
2. Quiet Sitting

After stretching or not stretching, the subjects underwent the following treadmill tests:

1. Run at 65% of maximal aerobic capacity (VO2max) for 30 minutes while energy-cost is measured.
2. After 2 minutes of rest and rehydration, run as far as possible in 30 minutes (subjects could control treadmill speed and see a time display, but not see a speed or distance display).

Experimental Results
On the no-strech day, the athletes performed significantly better as follows:

• They covered an average of 6.0 km in 30 minutes on the no-stretch day compared to 5.8 km on the stretch day
• They required an average of 425 calories on the stretch day vs. 405 calories on the no-stretch day to do the 30-minute submaximal run.

Bottom Line
Static stretching before running hurt the athletes' distance-running performance. After stretching they required more energy to run the same speed in the submaximal test, while in the maximal-distance 30-minute test they were not able to run as far. These differences can easily affect the chance of winning a race. The negative effect of static stretching appears to be due to a reduction in the spring-like stiffness of the leg muscles resulting in lower efficiency. Thus, it does not appear advisable to do static stretching before distance-running events. While dynamic stretching has not been subject to similar testing, it is a possible alternative. The evidence suggests that the best warmup before a distance-running event may be walking followed by jogging followed by short-distance runs at speeds increasing to race-pace.

Mixed-Intensity Interval Training vs. Steady-Speed Running

Evidence continues to pile up concerning the advantages of interval training. A study by James Clark in the Journal of Strength and Conditioning Research (vol. 24, no. 7, pp. 1773-1781, 2010) compared interval training comprised of runs of varying lengths and intensities to steady-speed running as to which produced greater improvements in maximal oxygen uptake (VO2max), the gold standard of aerobic fitness.

Study Procedure
The subjects were 32 female league and college competitive soccer players who were divided into 2 groups that trained as follows for 8 weeks:

1) Mixed-Intensity Interval Training (MIIT): The workout consisted of repetitions of the following 6-minute exercise cycle:

• 30 sec of jogging
• 30 sec running at 90-100% of max effort
• 60 sec of jogging
• 60 sec running at 80-90% of max effort
• 90 sec of jogging
• 90 sec running at 70-80% of max effort

      The subjects did 2 cycles (12 min) the first week and increased to 6 cycles (36 min) by the eighth week.

2) Steady-Speed Training (SST): They ran steadily at a "moderate to hard" pace (heart rate corresponding to 60-80% of that at maximal oxygen uptake). Run time was 40 minutes the first week and increased to 60 minutes by the eighth week.

Results
The mixed-intensity interval training group improved in maximal oxygen uptake by over 25% while the steady-speed training group improved less than 17%, a statistically significant difference.

Bottom Line
The mixed-intensity interval training improved aerobic fitness more than did steady-speed running, and required less time per workout. In addition, while it was not tested, it is likely that the sprinting segments of the interval training produced more improvement in sprinting ability, which is essential for soccer and other sports requiring bursts of speed. Thus, it appears that mixed-intensity interval training is advantageous for athletes in various team sports. Steady-speed running is still important for distance runners, who generally work out at various intensities during a training week.

NOTE: This description of experimental results is for informational purposes only and does not constitute a recommendation. Anyone engaging in an exercise program should obtain proper medical authorization before doing so.

Is Elliptical Training as Good as Running for Improving Fitness?

Elliptical trainers have become very popular in gyms as well as in the home. Their popularity is due to a lack of impact on the body while providing resistance to both the lower and upper body musculature. The movement pattern looks similar to running but does not involve pounding of the feet on the ground. An added advantage is the relative silence of an elliptical device compared to a treadmill, which produces considerable noise from foot strikes and its motor.

An important question is whether the elliptical trainer provides as good an aerobic workout as a treadmill or running outside. A study by Brown et al. in the Journal of Strength and Conditioning Research (volume 24, number 6, pp. 1643-1649, 2010) was designed to answer that question.

Experimental Procedure
9 male and 9 female college-aged subjects worked out for 15 minutes on different days on both a treadmill and an elliptical trainer at a difficulty level they self-selected as “somewhat hard.” The subjects were instrumented to collect information on their rate of oxygen utilization, pulse rate and other relevant variables.

Results
The only statistically significant differences between exercise on the elliptical machine and the treadmill were that the elliptical machine produced higher:

• heart rate
• percentage of maximal rate of oxygen utilization
• Ratio of carbon-dioxide produced to oxygen used

However, there were no significant differences in total energy expenditure or total oxygen consumption.

Bottom Line
The similarities between the responses to exercise on the elliptical trainer and treadmill were far more important than their differences. They both produced very similar aerobic stimulus to the body when the subjects worked out at a moderate level of difficulty, which is typical. Therefore, for general health, one can use an elliptical trainer with confidence. However, since running is a very basic human activity that is essential for sports and reacting to emergencies, run training is still generally more useful. Someone who trains exclusively on an elliptical machine and reaches a high level of fitness will not perform as well when faced with a running challenge, and muscle soreness will surely result. Yet, elliptical training is a good way to maintain cardio-respiratory function for injured athletes and others who cannot tolerate lower body impact. It can also provide variety in training for those who run regularly.

Static Stretching Reduces Jumping Power

Introduction
In static stretching, a muscle is stretched to the point of mild discomfort and the position is held for 15 sec or more. In contrast, dynamic stretching involves rapidly moving in and out of the stretched position. The former recommendation in favor of static stretching was based on the finding that it was effective for lasting improvements in flexibility. Thus, for many years, pre-competition static stretching was widely recommended for a broad range of athletes. However, recent studies, such as the one described below, have shown that static stretching before athletic efforts requiring explosive power (e.g. sprinting and jumping) actually hurts performance.

Study Methods
In a study by La Torre et al. (Journal of Strength and Conditioning Research, vol 24, no 3, pages 687-694, 2010), 17 young men performed vertical squat jumps from a force-detecting platform using various starting knee angles. On one day, they did the jumps after performing static stretches of their quadriceps and calf muscles for 10 minutes. Each muscle was stretched on both legs using 4 sets of 30-second holds with 30-second rests between sets. On another day they did the jumps without stretching beforehand.

Results
At all starting knee angles, stretching before the jump test reduced jump height, peak force, and maximal acceleration, but only the differences for jumps beginning with the knees least bent were statistically significant. When starting the jump with the knees flexed 50 degrees (about a half-squat position) jump height, peak force, and maximum acceleration were respectively 21%, 9%, and 15% lower when stretching was performed first than when no stretching was performed.

Bottom Line 
This study reinforces other ones showing that static stretching prior to an athletic event reduces explosive muscular power. The fact that the negative effect is most pronounced when the knees are only bent to a moderate degree is highly relevant to sports activities because most sports do not involve deeply bending the knee. Dynamic stretching does not have the same detrimental effect. Thus, it appears that before athletic events that require power but not great flexibility it is best to warm up thoroughly and perform dynamic stretches before the event. The detrimental effect of static stretching on muscular power has not been shown to carry over to the following day. Therefore, static stretching may be performed after an athletic event to promote general flexibility without harming physical performance.

Improving Performance in High-Level Athletes

Introduction
     It is not difficult to improve the physical performance of people who have had little or no intense training. Yet, it is much more challenging to improve the performance of high-level athletes who presumably have been training and competing at intense levels for considerable time. After all, their training and play have already stimulated their bodies to make major physiological changes, and many have likely reached a plateau by which they are no longer improving in their physical performance. However, a study by Wong et al. in the latest issue of the Journal of Strength and Conditioning Research (vol 24, no 3, 2010, pp. 653-660) shows that even the performance of professional athletes can be improved by a well-designed training program.

Experimental Methods
A group of Hong Kong professional soccer players were divided into 2 groups that trained for 8 weeks during the pre-season as follows:

• Group 1: made up of 20 players who engaged in strength training and high-intensity interval training twice per week in addition to their regular soccer training. The strength training consisted of 4 sets of 6 repetitions of high pull, jump squat, bench press, back half squat, and chin-up. The high-intensity intervals consisted of sixteen 15-second sprints at 20% faster than maximal aerobic speed interspersed with 15-second rest periods. The method for determining maximal aerobic speed was not clearly described. However, it might be taken as the fastest pace at which one can run 3-5 miles (5-8 km).
• Group 2: made up of 19 players engaged in only their regular soccer training.

Results
Only Group 1 improved significantly in the vertical jump (by 4%), 10-meter sprint time (by 6%), and 30-meter sprint time (by 3%).
Group 1 improved twice as much (20%) in a test of shuttle-running at progressively increasing speed as Group 2 (9%).

Bottom Line
Even high-level athletes can improve their physical performance by following a well-designed training program. Twice per week sessions of high-intensity interval training and weight training in addition to regular sport training appear effective for high-level athletes. It should be noted that this was pre-season training. Generally, during a competitive season, exercise other than regular sport-drills and competition is cut back considerably to avoid overtraining.

Medical Disclaimer
This description of experimental results is for informational purposes only and does not constitute a recommendation. Anyone engaging in an exercise program should obtain proper medical authorization before doing so.

An Effective Method for Improving Sprint Speed

Introduction
Resisted sprinting has become a standard training method for sprinters and other athletes who rely on their sprint speed (e.g. football players). There are various way to provide resistance to sprinting, such as small parachutes pulled by sprinters, push and pull sleds and carts, and long elastic cords. Evidence for the effectiveness of resisted sprinting, especially in combination with strength training, was provided in a recent article by Ross et al. in the Journal of Strength and Conditioning Research (vol 23, no 2, 2009).

Experimental Method
25 college-age male athletes (American football, soccer, track and field), were divided among the following 3 training groups, all of which trained for 7 weeks:

1. Resisted Sprint Training: Did 8-12 sets of 40-60-meter sprints on a treadmill with 2-3 minutes rest in between. A proprietary device pulled back on the sprinters with up to 25% of their bodyweight. 25-40% of the sprints in each training session were resisted and the rest were unresisted.
2. Strength Training: Did a split routine of 10 weight-resisted exercises two days per week and 9 other exercises two days per week plus a core circuit each workout. Each exercise was done for 3-4 sets of 6-10 repetitions. There were 26-30 total sets per workout in addition to the core circuit.
3. Combined-Training: Did both the Resisted Sprint Training and Strength Training programs described above, on different days.

Experimental Results

• Only the Combined-Training group improved significantly in 30-meter sprint time.
• The Resisted-Sprint Training group improved somewhat in 30-m sprint time, but the change did not quite reach statistical significance.
• Only the Combined-Training group improved significantly in treadmill sprint peak power.
• All 3 training groups significantly improved their maximum barbell squat (6.6-8.4 kg) without any statistically significant difference among the improvements of the groups.

Bottom Line:
Resisted Sprint Training, especially in combination with Strength Training, is effective in improving sprint time, even among athletes who are already practiced in their sports.

Heavy weight training improves running economy

Previous research has shown that weight-training improved the running economy of distance runners. To further explore this phenomenon, recent research was undertaken to find out if traditional weight training or explosive weight training had different degrees of effectiveness for increasing running economy. An article entitled, "Effects of strength training on running economy" by Guglielmo, Greco, and Denadai of the Human Performance Laboratory, UNESP, Rio Claro, Brazil, published in the International Journal of Sports Med. in January 2009, presented the results of a study. Sixteen well-trained runners engaged in either traditional heavy weight training or explosive weight training, all for 4 weeks on the same equipment. They were then tested while running on a treadmill to see how much oxygen per unit body weight they used to run at a set speed. Only the group that trained traditionally improved in running economy. The observed 7% increase in economy could translate to a marked increase in running speed sustained over a distance. This study demonstrates that weight training can be beneficial for endurance athletes as well as strength and power athletes.