For Pure Flexibility, Static Stretching Beats Dynamic Stretching

This blog contains several articles that have shown that static stretching impairs physical performance in jumping, running, and team sports, when the stretching is done immediately prior to the effort. Dynamic stretching has not been shown to cause a similar impairment and may even enhance performance. Yet, this finding does not mean that dynamic stretching is superior to static stretching for all purposes. Indeed, a study published by Covert et al. in the Journal of strength and Conditioning Research (vol. 24, no. 11, pp. 3008-3014, 2010) indicates that static stretching is better for improving pure flexibility.

Study Procedures
Over a 4-week period, 16 men and 16 women, aged 20-27 were randomly divided into the following 3 groups:
Static Stretching: Held a stretched position of the hamstring muscles for 30 seconds 3 times a week
Dynamic Stretching: Got into a stretched position of the hamstring muscles then performed small bounces into and out of that position at a rate of 1 per second for 30 seconds, 3 times a week
Control: Did not stretch
Hamstring flexibility was measured as the number of degrees short of 180 degrees that the knee could be extended to while the subject lay on a table with the thigh in a vertical position. Thus, a smaller number of degrees indicated better flexibility.

Results
The differences between changes in hamstring flexibility among all three groups were statistically significant
The control group declined by a mean of 3.3 degrees in hamstring flexibility
The static stretching group improved a mean of 11.9 degrees in hamstring flexibility
The dynamic stretching group improved a mean of 3.8 degrees in hamstring flexibility

Bottom Line
Either form of stretching improves flexibility. However, static stretching improves flexibility significantly more than does dynamic stretching. For sports in which flexibility in not very important, dynamic stretching is best. However, for sports which require a lot of flexibility (e.g. gymnastics, wrestling, high-hurdles) some static stretching is advisable. But because static stretching impairs performance when done immediately prior to the sport activity, it is best to do such stretching immediately following a training session, when the muscles are well warmed up. The impairment in performance caused by static stretching has not been found to carry over to the following day, so post-exercise static stretching should not impair a subsequent day's performance.

How Safe are Whole-Body Airport Scans?

In it’s December 13, 2010 issue, Newsweek published a chart comparing the radiation a person receives from the new full-body x-ray scanners in airports to other sources of radiation. The radiation levels are listed below:


Airport whole-body scan                            0.01 MREM
x-ray of extremity                                     0.10 MREM
Dental x-ray                                             0.50 MREM
Cosmic radiation, sea level                      24.00 MREM/year
Terrestrial radioactivity                             28.00 MREM/year
Mammogram                                          40.00 MREM
Cosmic radiation, Denver                         50.00 MREM/year
Radon in average home                         200.00 MREM/year
CT scan of abdomen and pelvis           1,500.00 MREM
Level causing radiation sickness      100,000.00 MREM

If the results are to be believed, and Newsweek usually carefully checks its sources, then the airport whole-body scans appear to be low-risk. That is not to say that they are without risk, because any radiation may bring some risk with it. Also, the comparison to environmental radiation exposure per year can be misleading because, when you go through a scanner, you receive the full dose of radiation in a few seconds, and the rate of exposure could be a factor in causing undesirable changes to body cells. For example, the sea-level cosmic radiation exposure per year translates to only 0.0000007 MREM per second. Nevertheless, the exposure from an airport scanner appears far less than that from a dental x-ray, which most of us accept as part of our health maintenance. An additional factor is that the genitals, which are particularly vulnerable to radiation, are usually shielded when health-related x-rays are taken. Since the “underwear bomber” prompted the scans in the first place, the genitals can not be shielded in such scans. At this point, the scans appear safe, but each individual must decide whether or not a body pat-down is preferable to a scan.

Men's Health Fit?

There was an article in Men’s Health Magazine’s November 2010 issue entitled, “Are You Men’s Health Fit?”. The article highlighted four elite athletes from different sports and presented seven physical fitness tests, stating that, if you can achieve the highest level on each test, you are “Men’s Health Fit“. Below are the tests along with the Men’s Health standards and my comments.

1. Test - Timed Plank:
The body, face down, is held in a straight line with the toes and forearms on the ground.

• Below average: Plank with elbows directly below shoulder’s held for less than one minute
• Average: Plank with elbows directly below shoulder’s held for one minute
• Above average: Plank as above but with feet on a bench (of unstated height) held for one minute.
• Men’s Health Fit: Plank with feet on floor and elbows below eyes held for one minute.

2. Squat while holding a wooden stick overhead with hands spaced 1.5 times shoulder width:

• Below average: You can’t bend your knees to 90 degrees without leaning forward
• Average: You can only bend your knees past 90 degrees if your heels come off the floor
• Above average: You can do a full squat while keeping your heels on the floor and not leaning forward
• Men’s Health Fit: You can do the above while holding a 45-lb bar instead of the stick.

My Comments:
This is a test of flexibility of the calf muscles, shoulder, and back rather than a physical fitness test. It’s hard to see how the ability to do this would relate to sports performance or any physical challenge other than Olympic weightlifting, which requires this specific kind of flexibility.

3. Barbell dead lift:

• Below average: less than bodyweight
• Average: 1-1.25 times bodyweight
• Above average: 1.25-1.5 times bodyweight
• Men’s Health fit: more than 1.5 times bodyweight

My Comments:
To define levels in terms of proportion of bodyweight lifted is naïve because, for physiological and biomechanical reasons, smaller people can lift more in proportion to their bodyweight. The following standards from exrx.net show how body size affects standards:

                                     Deadlift as Proportion of Bodyweight
Bodyweight (lb)    untrained     novice    intermediate   advanced   elite
        148                 .85             1.58           1.82           2.57       3.26
        181                 .82             1.51           1.74           2.42       3.03
        220                 .75             1.39           1.60           2.18       2.66

Based on the table, the standards given by Men’s Health are low for anyone who trains with the deadlift exercise.

4. Standing broad jump:

• Below average: less than 6 feet
• Average: 6-7 feet
• Above average: 7-8 feet
• Men’s Health fit: more than 8 feet

My Comments:
There are few published adult norms for the standing long jump. However, a study by Santilla et al. in Medicine and Science in Sports and Exercise (vol. 38, no. 11, pp. 1990-1994, 2006) presents the following as military standards in Finland.

• Poor: less than 6’7” (2.0 meters)
• Satisfactory: 6’7” (2.0 meters)
• Good: 7’3” (2.2. Meters)
• Excellent: 7’ 11” (2.4 meters)

The “Men’s Health Fit” standard seems a reasonable approximation of “excellent“. However, the “below average” standard should be higher and the lower limit of the “average” range should be higher. One problem is that jumping ability is largely related to the percentage of fast-twitch fibers in one’s leg and hip muscles, which is determined mainly by heredity. Thus, only a limited degree of improvement can be expected from training.

5. Pushups:

• Below average: less than 15
• Average: 16-29
• Above average: 30-44
• Men’s Health fit: 45 or more

My Comments:
The magazine’s pushup standards are quite low. The following standards for males aged 20-29 were published by the American College of Sports Medicine (see our website for the full table):

• 25th percentile: 24
• 50th percentile: 33
• 75th percentile: 44
• 90th percentile: 57

The Army standards (age 22-26) are even tougher because soldiers know they will be tested every 6 months and many of them train for the test:

• 60 points (just passing): 40
• 75 points: (average): 53
• 90 points (excellent): 66

6. Chinups (undergrip) pausing 1 sec at top:

• Below average: less than 3
• Average: 3-7
• Above average: 8-10
• Men’s Health fit: more than 10

The Marine Corps scores the pullup segment of its physical fitness test for men aged 17-26 as follows:

• 3rd class (passing): 9
• 2nd class (good): 12
• 1st class (excellent): 15

The Men’s Health standards are low in comparison to the Marine Corps standards. Of course, Marines are tested regularly for the number of pullups they can do, so they train at the exercise.

7. Mile Run:

• Below average: 12 or more minutes
• Average: 9-12 minutes
• Above average: 6-9 minutes
• Men’s Health fit: under 6 minutes

My Comments:
Adult norms for the 1-mile run are not readily available. However, the following 1.5 mile run standards for males aged 20-29 were published by the American College of Sports Medicine (see our website for full table):

• 25th percentile: 13:53 (9:15 mile pace)
• 50th percentile: 12:18 (8:12 mile pace)
• 75th percentile: 10:42 (7:08 mile pace)
• 90th percentile: 9:09 (6:06 mile pace)

The Army standards (age 22-26) are even tougher at the low end because soldiers know they will be tested every 6 months and most of them train for the test:

• 60 points (just passing): 16:36 (8:18 mile pace)
• 75 points: (average): 15:15 (7:38 mile pace)
• 90 points (excellent): 13:54 (6:57 mile pace)

Since these standards are for the 1.5 and 2.0 mile run, the same populations would run the mile run at an even faster pace. While the pace needed to be “Men’s Health Fit” would be considered excellent by either standard, the magazine’s standards for average and above average are far too slow.

Conclusions:
It’s difficult to ascertain how Men’s Health Magazine decided which tests were important and where it got its standards, many of which seem arbitrary. They’re low for the deadlift, pushups, and chinups, and low for the lower fitness levels in the standing broad jump and mile run. Since there are no references for the standards in the article, one might think that they were developed by group consensus among the magazine’s staff members.

One factor that the article ignores is that there are different types of athletes who, because of their body types and natural talents, excel at different sports. Elite athletes are very specialized creatures. Strength and power athletes do not generally do very well on tests of whole-body endurance while endurance athletes often do poorly on strength and power tests. Thus, it is likely that the four athletes highlighted in the article would excel at some tests and do poorly on others. It is misleading to imply that one has to do well on all types of fitness tests to be a good athlete.

By calling the highest level on each test the “Men’s Health Fit” standard, the magazine seems to be sending the message that it has very tough standards, even leading one to surmise that the magazine’s staff members are all super-fit. It would be very interesting to see how its staff would do on the tests. It would be surprising if any of them could score “Men’s Health Fit” on all the tests.

More Evidence in Favor of Post-Activation Potentiation (PAP)

We have previous discussed post-activation potentiation (PAP) by which an explosive athletic performance is improved by doing heavy resistance exercise beforehand (see http://mens-fitness-and-healthdotcom.blogspot.com/2010/10/method-for-improving-explosive-physical.html).  A recent study provides further evidence of the effectiveness of this technique.

Matthews, Comfort and Crebin performed a study on ice hockey players from the English National League.

Experimental Procedure
On two different days, 11 players were timed for their maximal 25-meter sprint-speed on ice both before and 4 minutes after doing the following:

1. resting
2. sprinting while towing another skater

Results

• When the players rested between sprints, they showed no significant improvement in time between their first and second sprints.
• When the players skated against resistance following the first sprint, their second sprint took a significant 2.6% less time than their first one.

Bottom Line
This study supports others that have found improvement in explosive athletic performance when heavy resistance exercise is performed first. The resistance exercise should call upon the same muscles used in the athletic performance. Using resisted skating in this study was a good way to achieve this goal.

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.

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.