The Drawback of Exercising on Unstable Surfaces



Stability training, mainly in the form of lifting weights while standing on unstable surfaces, became somewhat popular with the advent of the Bosu Ball, which is a hemispheric ball about 2+ feet across mounted on a flat plastic base. The idea is that the instability of the surface brings muscles into play that are required for maintaining stability; muscles that would be minimally involved when exercising on a stable surface.

A study by Chulvi-Dedrano et al. in the Journal of Strength and Conditioning Research (vol. 24, no. 10, pp. 2723-2730, 2010) tested force production and muscle electrical activity during deadlifts on a stable surface and on two different unstable surfaces.

Method
31 young adult subjects did the following:

1. Isometric deadlift in which the lifter pulled upward maximally for 5 seconds against an immovable bar
2. Dynamic deadlift in which a barbell weighing 70% of the individual’s maximal isometric deadlift was lifted for 5 repetitions 

Lifting force was measured during the isometric efforts. Muscle electrical activity of the lower back muscles (paraspinals) was measured during both the isometric and dynamic lifts to indicate how hard the muscles were working. Both of the lifts were done on the following 3 surfaces:

1. Stable floor
2. Bosu Ball
3. T-Bow (a curved board that can rock laterally as one stands on it)

Results

• In the isometric deadlift, both the force produced and the muscle electrical activity were significantly higher on the stable surface than on either unstable surface.
• In the dynamic deadlift, muscle electrical activity was significantly higher on the stable surface than on either unstable surface

Bottom Line
This study backs up other ones that have shown that exercising on unstable surfaces does not provide as much stimulus as stable-surface training to the main muscles (prime movers) used to effect the exercise movement. It has previously been shown that more weight can be handled when lifting on stable than unstable surfaces, providing greater stimulus to the muscles. In view of these factors, training on unstable surfaces is not best for increasing the size or strength of the major muscles. However, since such training does bring stability muscles into play, it can be effectively used as a supplement to training on stable surfaces, especially for athletes who engage in sports in which maintaining stability is of major importance (e.g. hockey, figure skating, snow-boarding, gymnastics). The major part of the resistance workout should still be on stable surfaces.

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.

Dynamic Stretching Beats Static Stretching for Team Sports

Introduction
Static stretching involves attaining a stretch to the point of mild discomfort and holding the position for at least 10 seconds. Dynamic stretching involves rapid repeated alternation between a stretched and a relaxed position.

A recent article by Amiri-Khorasani et al. in the Journal of Strength and Conditioning Research (vol. 24, no. 10, pp. 2698-2704, 2010) showed that static stretching detracts from performance on a physical agility test, while dynamic stretching tends to improve it.

Method
Nineteen professional soccer players were divided into more-experienced and less-experienced subgroups. Their performance on an agility test, which involved 14-15 seconds of changing direction and zigzagging as fast as possible around a number of cones, was tested after each of the following:

• No stretching
• Static stretching
• Dynamic stretching
• Combined static and dynamic stretching

Results

• The subjects were 4-5% slower after static and combined static/dynamic stretching than they were with either no stretching or dynamic stretching alone.
• Among the less-experienced players, dynamic stretching resulted in about 3% faster course times than no stretching.
• Among the more experienced players, there was no difference between the course times after dynamic stretching and no stretching.

Bottom Line
The evidence indicates that dynamic stretching is superior to static stretching for the kind of agility needed for most team sports. This is probably due to a reduction after static stretching in the spring-like stiffness of muscle. The results support those of other studies that have shown a detrimental effect of static stretching on strength, jumping ability and sprint speed. It is not clear why the experienced players in this study showed no advantage of dynamic stretching over no stretching at all. However, since these were professional soccer players, it seems safe to conclude that the effects on amateur athletes would parallel those on the less experienced professional players. Thus, their performance would likely be enhanced by dynamic stretching.

Plyometric Training for Improved Sports Performance

Plyometric training has been popular among strength and physical conditioning coaches for a number of years. Yet many people who exercise on their own are not familiar with this method. Simply put, plyometric exercise involved rapid stretch and shortening of a muscle. This occurs in such movements as hopping, jumping, and bouncing. For example, when you jump vertically, you naturally first do a countermovement in which you bend your knees quickly while stretching your quadriceps (front thigh) muscles, then rapidly contract those muscles to straighten the knees and propel the body upwards. Thus, repeated vertical jumps are one kind of plyometric exercise.

There are various gradations of plyometric exercise, and it is considered prudent to start with low-stress ones before progressing to more difficult ones. One of the most stressful plyometric exercises is depth-jumping, in which one jumps down from a box and, after contacting the ground, immediately jumps vertically. This is considered dangerous for anyone who does not already have a strong lower body and has not progressed from low-stress, through moderate-stress, to high-stress plyometric exercise. Various sources have recommended being able to squat with 1.5 times one’s bodyweight before taking on a serious plyometric exercise program. However, it is generally considered safe for people in good health without orthopedic problems to perform low-stress plyometric exercises like low bounces, hops, and jumps.

A recent study by Chelly et al. in the Journal of Strength and Conditioning Research (Vol 24, no. 10, pp. 2670-2676, 2010), showed how effective plyometric training can be.

Method
A group of experienced young male soccer players, average age 19 years, trained as follows:

• August - preseason training consisting of light resistance exercise and calisthenics
• September through March (the competitive season) - The players trained 5 days per week for 90 minutes by doing skill and tactical drills along with 30 minutes of continuous play. On one day per week they engaged in a competitive soccer game against another team.

The subjects were divided into 2 groups:

Group 1 only did the training program above.
Group 2 did the training program above plus from January-March they also did the following plyometric training twice per week:

• Week 1: 5 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
• Week 2: 7 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
• Week 3: 10 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
• Week 4: 5 sets of jumping over ten 60-cm (36“) hurdles spaced 1 meter (39.4”) apart
• Week 5: 4 sets of depth-jumps from a 40-cm (24“) box
• Week 6: 4 sets of depth-jumps from a 40-cm (24“) box
• Week 7: 4 sets of depth-jumps from a 40-cm (24“) box
• Week 8: 4 sets of depth-jumps from a 40-cm (24“) box

Extensive testing on speed, power, and jump height was performed before and after the training.

Results

The group that did regular soccer training did not show significant improvement in any of the pre-post tests.

The group that did plyometric training in addition to their regular soccer training showed the following statistically significant improvements:

• Thigh muscle volume: +2.5%
• Cycle ergometer absolute power: +4.5%
• Cycle ergometer power relative to body mass: +5.9%
• Jump height without a countermovement: +8.3%
• Jump height with a countermovement: +2.5%
• 40-meter sprint first step velocity: +18.2%
• 40-meter sprint velocity over first 5 meters: +10.0%
• 40-meter sprint velocity between 35 and 40 meters: +9.8%

Bottom Line
Although not all studies of plyometric training have produced improvements of this magnitude, it appears that the evidence supports inclusion of plyometric exercise in physical training programs for sports involving sprinting and/or jumping.

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.

A Method for Improving Explosive Physical Performance

Introduction

Post-activation potentiation (PAP) is not a training method. Rather, it is a method for improving performance in an explosive activity (e.g. jumping, sprinting) by doing heavy exercise with relevant muscles (e.g. squats) shortly before the performance. Several studies using either weight-resisted or isometric exercise have shown a positive effect on performance. One such study, by Berning et al. is described in the Journal of Strength and Conditioning Research (vol. 24, no. 9, 2010, pp. 2285-2289).

Methods

Subjects:

• Group 1 - Thirteen trained young men who had been squatting at least twice a week for at least one year.
• Group 2 - Eight untrained young men

The subjects in both groups were first tested for the maximum amount of weight they could parallel squat for a single repetition. That involved squatting down with a barbell on the shoulders from a standing position until the thighs were parallel to the ground, then standing up again. On other days, each group did the following:

• On one day they did 5 minutes of low intensity cycling followed by maximal vertical jump testing.
• On another day they did 5 minutes of low intensity cycling, then a functional isometric squat followed by maximal vertical jump testing. For the functional isometric squat, a barbell containing 1.5 times the subjects’ maximal weight for the parallel squat was placed on supporting rods in a squat rack. A second set of rods was positioned about 4” higher than the first set. The lifter got under the bar so that it rested on his shoulders then drove the bar vertically against the upper set of rods as hard as possible for 3 seconds before placing the bar back to the lower set of rods. The positioning of the rods was such that the subject lifted from a half-squat position. The subjects could lift much more weight than they could in a full squat because of the more advantageous leverage in the half-squat than the full-squat.

Results

• Among the untrained men, the functional isometric squat performed before the jump test did not provide any advantage.
• Among the trained men, the functional isometric squat performed before the jump test led to significantly higher jump height, and the effect was retained when they were again tested 5 minutes after the lift. The magnitude of improvement in jumping was about 5% (2.4 cm ~ 1”).

Bottom Line

Post-activation potentiation (PAP) is a phenomenon with a fair degree of experimental support. It can be applied to any athletic activity in which a maximal explosive effort can be conveniently preceded by a heavy squat with a barbell, or even an isometric squat against an immovable object. Such athletic activities include but are not limited to high-jump, long-jump, track sprint, Olympic weightlifting, and Highland Games contests. It remains to be seen if the method can be applied to other athletic activities such as baseball hitting, football kicking, or wrestling. The method does not appear applicable to sports involving exertion over a relatively long period of time such as soccer, basketball, or hockey.

NOTE: This description of experimental results is for informational purposes only and does not constitute a recommendation. Heavy barbell squats should only be performed by experienced lifters. The supportive muscles, tendons, and ligaments involved must be developed using a consistent training program over an extended period of time. Anyone wishing to engage in strenuous physical activity must first determine if it is safe to do so. A physician’s clearance is always the best means of determining if you are healthy enough to exercise. Our exercise risk factor questionnaire can help you estimate your risk.

You May Not Be Getting Enough of These Nutrients

An article in the September 2010 issue of the Nutrition Action Health Letter contains a cover story entitled, “Getting Enough? What you don‘t eat can hurt you.” The article states that many of us are not getting enough potassium, magnesium, Vitamin D, or Vitamin B-12, with possible negative health consequences.

Potassium

• A third of Americans have high blood pressure, which increases the risk of heart attack and stroke. Over age 65, two-thirds of us have high blood pressure. More than half of those afflicted don’t have it under control.
• Potassium can help regulate blood pressure. Major studies have shown that people with higher potassium intake have lower blood pressure.
• A low potassium level is a predictor of stroke. A study of 43,000 subjects showed that those consuming the most potassium had 38 percent fewer strokes that those who consumed the least. The beneficial effect of potassium is the greatest for those who consume the most sodium. It is thought to work by increasing the flexibility of arteries and widening the tiny blood vessels.
• While blood pressure typically rises as one gets older, 4 weeks on a low sodium, high potassium diet can totally reverse the effect of age on blood pressure. The DASH Diet (Dietary Approaches to Stop Hypertension), which minimizes added salt and includes 11 daily servings of fruit and vegetables as well as 2 servings of low-fat dairy products and low quantities of saturated fats, refined sugar, and refined grains, provides plentiful potassium while keep sodium down to recommended levels.
• Potassium citrate is the form of potassium found in fruits and vegetables and it is considered more effective for blood-pressure reduction and safer than potassium supplements (usually potassium chloride), which can cause heart problems if taken in excess. Potassium citrate also reduces the risk of kidney stones by 50% and may help prevent bone loss.

 Vitamin D

• This nutrient seems more important than calcium for protecting bones and preventing osteoporosis, a  bone-thinning disease that causes bone fractures in 25% of men and 50% of women over age 50.
• Among Navy recruits, supplementation of 2,000 mg of calcium along with 800 IU of vitamin D per day reduced stress fractures by 20%.
• Evidence suggests that Vitamin-D also protects against colon cancer, heart atacks, stroke, diabetes, falls, autoimmune disease, and all-cause mortality.
• The article recommends taking a Vitamin-D supplement, as it is difficult to get the recommended amount from food. The recommended dosage is 400 IU per day for people under 60 and 800-1000 IU per day for people over 60.
• Recommended calcium intake is 1000 mg/day for people under 50, and 1200 mg/day for people over 50.

Magnesium

• Many Americans have Type II diabetes, including 25% of people over 60.
• Diabetes greatly increases the risk of stroke, heart disease, blindness, kidney failure, nervous system damage, and limb amputations.
• While excess body fat, lack of exercise, and poor eating habits are the major risk factors for Type II diabetes, a lack of magnesium can be a contributing factor. Large studies have shown that high magnesium intake is associated with reduced incidence of diabetes.
• Fruits, vegetables, whole grains, nuts and beans are plentiful in magnesium. 

Vitamin B-12

• Low levels of Vitamin B-12 are associated with poorer memory and mental ability. Yet the ability to absorb this vitamin from food decreases as we age.
• A low Vitamin B-12 level in combination with a high levels of folic acid is strongly associated with cognitive impairment.
• The article recommends taking a multivitamin containing at least 6 micrograms of Vitamin B-12 or a B-12 supplement containing up to 100 micrograms of B-12, and being careful not to get too much folic acid from vitamins and fortified cereals.

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.