Exercise is Associated with Better Eating Habits in Children

A recent study at Blaise Pascal University and Clermont University in France explored the relationship between poor eating behaviors and exercise in 278 children (147 girls) between the ages of 6 and 10. The researchers measured height, weight, body mass index, an adiposity index from skinfold measurements, and two measures of fitness: a 20-meter shuttle run and a squat jump test for height.  They identified the following eating behaviors as “high risk” when they occurred frequently: skipping breakfast; snacking; TV viewing during meals; and sweetened beverage consumption. Dietary habits were obtained from a validated questionnaire completed by parents in the present of the child.  106 children presented with one risk factor, 46 children had 2 eating risk factors, and 20 had at least 3 factors. Children who ate breakfast every day were fitter than those who ate breakfast sometimes or never.  Children who snacked everyday had significantly lower vertical jumps than those who rarely or never ate breakfast.  These results were independent of obesity.

The bottom line of this research is that unhealthy eating habits in elementary school children appear to be associated with poorer fitness. The authors believe that progressive lifestyle interventions which change a child's eating habits step by step may lead to progressive improvements in physical fitness.

Read more about the study here.

Running on the Moon

One of the key questions that remains unanswered as we prepare to send humans to other planetary surfaces is the degree to which living and exercising in these reduced gravity environments will provide an osteoprotective stimulus to prevent bone loss that is currently seen on International Space Station missions. 

With support from the National Space Biomedical Research Institute and the NASA Flight Opportunities Program, our research team from the Department of Orthopaedics and Sports Medicine at the University of Washington conducted a parabolic flight experiment to validate the activity monitoring system that was worn by subjects exercising in microgravity.  Nine subjects were tested as they performed a series of locomotor activities with the sensors positioned on the mid-lower back and around the ankle. Subjects were secured to the surface of the treadmill via a subject load device to provide loads similar to those experienced on Earth. Over two flight campaigns, activities were performed in three conditions:  zero, lunar, and Martian gravity.  An image of a subject running in zero-G with a simulated lunar load is shown below. 

With the acquired parabolic flight data, the team is developing classification software to autonomously recognize activities performed in reduced gravity.  Validation of this system would improve the ability to monitor exercise designed to preserve the bone health of astronauts aboard the ISS and on future exploration missions.  Similar methods could be applied to address the prevention of osteoporosis on Earth.

ACL Injury and the Menstrual Cycle

It has long been known that women have a highly elevated risk for rupture of the anterior cruciate ligament (ACL) in the knee compared to men engaged in the same activity. One of the many theories to explain this risk is that the increase in circulating estrogen and degrease in progesterone during the pre-ovulatory stage of the menstrual cycle reduces the strength of the ligament. A group of researchers from the Nollet Musculo-skeletal System Institute in Paris studied 172 pre-menopausal women (mean age 34 years) with regular cycles who tore their ACL while skiing. The accidents mainly occurred on blue (moderately difficult) slopes at medium speed and the ski bindings did not release in most patients.  The authors found that ACL injury was 2.4 times more likely to occur in a pre-ovulatory phase of the cycle compared to the post-ovulatory phase. This pattern was not affected by the use of oral contraceptives. 

Bottom Line:    The findings suggest that women engaged in risky recreational exercise during the pre-ovulatory stage of their menstrual cycles could decrease their risk of injury by taking special precautions.  In skiing this might involve skiing on less demanding runs and adjusting release bindings to a lower threshold.  Read more about the study published in the June 2013 issue of the journal Orthopaedics and Traumatology, Surgery and Research here. 

Optimizing Your Workout Schedule

The ideal balance between aerobic and strength training is a topic of controversy.  As an endurance athlete, it is often difficult to find the motivation to fit weight lifting into the schedule.   However, especially for older women (and even for younger ones), there is evidence that such exercise will strengthen the skeletal system and prevent osteoporosis.

Researchers at the University of Alabama at Birmingham studied 72 women between the ages of 60 and 74 years old.  The participants were divided into the following groups:

A.      1 day per week of aerobic and 1 day/week of resistance exercise

B.      2 day per week of aerobic and 2 day/week of resistance exercise

C.      3 day per week of aerobic and 3 day/week of resistance exercise

Surprisingly, group B appeared to experience the greatest increase in energy expenditure per day.  However, all three groups became stronger and more aerobically fit in addition to reducing their fat mass.  The conclusions of this experiment imply that if weight loss is your goal, a moderate exercise program, with both aerobic and strength training, may be your best bet!

Read the abstract here.

High-Heeled Shoes may Affect Long Term Muscle Efficiency and Function

While high-heeled shoes may be a fashionable choice of footwear for many women, habitual use of these shoes increases the risk of muscle fascicle strains and comprised muscle efficiency.  The structure of the shoe forces the foot into a plantar-flexed position.  This unnatural positioning of the foot shortens the medial gastrocnemius muscle fascicles and increases Achilles tendon stiffness.

Researchers at University of Jyväskylä in Finland and the Griffith University in Queensland, Australia studied 19 women, 9 of whom habitually wore heels (at least 40 hours per week over a minimum of 2 years) and 10 of whom rarely wore heels (less than 10 hours per week).  In addition to altering the length and stiffness of lower extremity muscles, habitual wear of high-heeled shoes increased the muscle activation of the tibialis anterior and soleus when walking in heels.  This increased level of activation is associated with decreased muscle efficiency.   When walking barefoot, the high-heeled shoe group exhibited higher muscle activation of the medial gastrocnemius during the stance phase of walking.  This trend indicates a chronic response to compensate for the altered muscle-tendon function.

Bottom line: It may be wise to limit the use of high-heeled shoes to special occasions in order to prevent chronic damage to the muscles and tendons that contribute to walking.

Read more about this study here.

ACL Injuries and Muscle Strength in Girls at Puberty

There are many theories and a vast medical and scientific literature exploring why girls who play sports experience more ACL injuries than boys.  A recently published review in the journal Sports Medicine authored by researchers from the University of Wollongong in Australia focused on changes in the relative strength of hamstring and quadriceps muscle at the time of puberty.  The evidence suggests that in girls during puberty the growth in size and strength of the hamstring muscle group seems to lag behind that of the quadriceps muscle group. This lag is not present in boys.

These observations have been made from retrospective studies (looking backwards at injuries) and scientists put the highest value on prospective studies (which look forward) in order to avoid bias.  However, the evidence seems strong enough to suggest that training which develops a greater balance between the hamstrings and quadriceps might be useful as a component of programs to help avoid ACL injuries in girls at puberty.

Read more about this review here.

Exercise and Breast Cancer Risk

It is now known that physical activity reduces the risk of breast cancer but the exact relationship between “dose” and timing of exercise  - particularly in relation to menopause – is less well defined.   A new study from the Department of Epidemiology at the University of North Carolina was recently published on-line in the journal Cancer.

The study examined these relationships in more than 1500 women with breast cancer and 1200 controls who did not in the Long Island Breast Cancer Study Project

The results indicated that exercise had no preventative effect when the onset of breast cancer prior to menopause was examined.  However, lifetime exercise was strongly related to cancer-free survival when breast cancer onset after menopause was examined. Child-bearing women who had exercised between 10-19 hours per week prior to and after menopause experienced a 30% reduction in the risk of breast cancer.  Surprisingly, exercise intensity did not seem to affect the relationship.  The data indicated that substantial postmenopausal weight gain may eliminate the benefits of regular exercise.

These results are strong evidence that exercise and weight maintenance are powerful factors in the prevention of breast cancer.

Read more about the study here.