Search This Blog

Thursday, December 30, 2010

Eating Nuts Provides Several Health Benefits

An article in the January 2011 Harvard Health Letter listed several health benefits of eating nuts. Although the calories in nuts come mainly from fat, the type of fat is largely of the unsaturated healthful variety. The article cited a study done at the Beth Israel Deaconess Medical Center showing that walnuts eaten at breakfast made subjects feel more full before lunch, potentially reducing caloric consumption. Other health benefits include favorable effects on blood cholesterol, blood pressure, and inflammatory factors. Studies on large populations have linked high nut consumption with lower heart disease rates. Nuts also contain little or no carbohydrate so they do not cause spikes in blood sugar and may even blunt blood sugar spikes caused by carbohydrates eaten along with the nuts. Peanuts, almonds, and pistacios have the highest protein content, while brazil nuts, cashews, hazelnuts, and walnuts have intermediate protein content, and pecans and macadamias have the lowest protein content. Walnuts have the additional benefit of being high in omega-3 fatty acids, which are widely considered the most healthful kind.

Wednesday, December 22, 2010

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.

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.

Insurance Institute for Highway Safety Top Safety Picks for 2010

BMW 5 series
(except 4-wheel drive and V8)
Infiniti M37/M56
(except M56x 4-wheel drive)

Honda Civic
4-door models (except Si)
with optional ESC
Kia Forte sedan
Mitsubishi Lancer sedan
(except 4-wheel drive)
Subaru Impreza
(except WRX):
sedan | wagon
Volkswagen Golf
4-door models
Volkswagen GTI
4-door models
Ford Fiesta
built after July 2010:
sedan | hatchback

Audi A4 sedan
Chrysler 200
4-door models


Kia Sorento
built after March 2010

Jeep Patriot
with optional side torso airbags

Tuesday, December 21, 2010

Are There Hidden Causes of the Overweight Epidemic?

In the December 20, 2010 issue of Newsweek magazine, Sharon Begley, the magazine’s science columnist, wrote that there are some little-known factors that may contribute to the continued increase in the prevalence of overweight and obesity. Her main argument is that it must be more than a matter of exercising more and eating better because, among animals that have contact with human beings, such as pets, lab animals and rodent pests, 23 of the 24 species studied since 1940 have shown significant increases in the percentages of overweight and obese animals, a statistic that could have occurred by chance only once in 8 million. Yet changes in diet and exercise don’t appear to be the reason, as these factors haven’t changed much for these animals over the years.

Begley cites some possible reasons other than diet and exercise for the weight gain of animals and, by extension, us:
  • The type of bacteria in our gut - more efficient bacteria wring more calories out of our food than do less efficient bacteria. In this case, efficiency is not our friend.
  • Lack of sleep, which increases the appetite-stimulating hormone ghrelin, and decreases the hormone leptin that suppresses our appetite when we’ve eaten enough.
  • Environmental chemicals such as BPA that stimulate fat-cell production.
  • Home heating, which lessens the need for the body’s calorie-consuming heat production.
  • Home air conditioning, which lessens the appetite-suppressing effect of environmental heat.
  • Infection with adenovirus-36, which causes obesity in  lab animals and is correlated with obesity in humans.
In addition, I feel that there may be another contributor to obesity:
  • The lack of internal parasites due to modern sanitary practices. If parasites eat some of our food, less of it can be packed on as fat. If they partake of our bodies, then energy must be consumed for repair. This assumes the kind of parasites that are relatively harmless other than consuming some of our food or body tissue.
Bottom Line
There is no doubt that our health benefits from exercising regularly and eating a healthy diet without excess calories. However, we must continue to look for other contributing factors in order to effectively deal with and counteract the continued rise in overweight and obesity that threatens to undermine the gains we’ve made in improving our health and increasing our lifespan.

Friday, December 10, 2010

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.

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.

Wednesday, December 8, 2010

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 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.

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.