WENDY SWEET
Why fitness matters Understanding the difference between “activity” and “fit”
As
the New Zealand government tries to mitigate obesity and diabetes in our children, it is timely to remind health and PE teachers of the health benefits of “improved fitness.” I use the term “fitness” purposively. It is a term that is absent from the youth obesity and diabetes discourse, as the preferred terms “physical activity and movement skills” have prominence. Yet, the difference between being “physically active” and “physically fit” is important from a bio-medical perspective. The changes that accrue from a certain “dose” or Frequency, Intensity, Time and Type (The FITT Principle, taken from the pioneer of exercise physiology, Robert Fitt’s) of cardiovascular and strength activities elicit a metabolic “response” that eventually contributes to physiological improvements in the cardiovascular system and skeletal muscle. The adaptations that occur from a progressive and accumulative approach to better fitness enable morphological improvements in cardiac and skeletal muscle, which decreases diabetes and obesity.
Teachers Matter
R.H. Fitts, an exercise physiologist, shaped much of the current thinking regarding exercise training and “dose-response” relationships in the ’70s. Fitts and other exercise physiologists found that exercise duration as well as intensity resulted in positive changes in muscle oxidative capacity. This is an important issue for heath and PE teachers to re-visit, as it is the impairments in skeletal muscle mitochondrial function and lipid (fat)
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oxidation that are known to play a significant role in metabolic problems such as insulin resistance, obesity and Type 2 diabetes. As well, new research on strength training also shows a protective role in Type 2 diabetes, although how this occurs is not fully understood. Understanding the role of the mitochondria is essential for anyone involved in promoting and supporting cardiovascular and musculoskeletal fitness gains. Mitochondria are organelles within skeletal muscle that can impressively boost a muscle’s capability to burn fat, improve insulin sensitivity, minimize fatigue and enhance capacity to synthesize fuel for physical activity and exercise (Menshikova et al., 2007). Kravitz reports that those who participate in regular endurance exercise increase the density and size of the mitochondria thus improving their ability to utilise more fat and use less carbohydrate for fuel during exercise. A secondary effect is the reduction in metabolic acidosis (lactic acid) produced in the muscles enabling the exercising body to do more work, experience less fatigue and burn more calories with each workout. All of these capabilities by the mitochondria are referred to as “mitochondrial biogenesis.” The question: How much exercise is enough to produce these necessary biological changes? Va n d e r H e i j d e n ’ s 2 0 0 9 s t u d y o f cardiovascular training in obese postpubescent youth provides some insight into the intensity debate. Twenty-nine subjects
(both male and female) underwent 12 weeks of supervised aerobic training (four sessions of 30 minutes each session) and wore heart rate monitors in an attempt to keep them exercising at an intensity of 70 percent of their aerobic capacity, a moderate intensity. The control group was lean subjects. The findings supported a 14 percent decrease in insulin concentration in the obese group compared to only 8 percent in the lean group; 3 percent decrease in percentage body fat in the obese group, and no change in the lean group. In a study of previously sedentary adults, Menshikova et. al (2007) also showed that moderate intensity aerobic exercise, four to six times per week and progressing from 30 – 40 minutes per session for 16 weeks resulted in significant mitochondrial biogenesis adaptations. The obese subjects in this study were also placed on a 25 percent calorie reduction diet. They averaged a 7 percent loss in body weight.
Fitness and academic achievement Studies involving public school students in California found a distinct connection between fitness and ability in reading and maths. Higher achievement was associated with higher levels of fitness, and the relationship between fitness and mathematical achievement was strongest.