Book Review: Sports Endocrinology by Michelle Warren and Naama Constantini

While you spend your free time reading Fifty Shades of Grey (come on, admit it. I know you do), as a self-professed geek, I spend my free time reading Sports Endocrinology by Michelle Warren and Naama Constantini.

Original source: here.

            Why?

Because I wanted to know in greater detail how sports affect hormones, and likewise, how hormones affect sports.

Here are some cool insights I gained from the book:

• You know how exercise releases endorphins (those feel-good chemicals that make you feel amazing)? Well, that only happens when the intensity is high enough. How high is high enough? Whether you’re doing endurance training or strength training, you need to cross the anaerobic threshold. That’s the point where your muscles burn.
  • In one experiment, when participants exercised at low intensities (for my fellow geeks, that’s at 25 and 50% of their VO2max, or maximal oxygen consumption), the feel-good endorphins didn’t rise. At all. When they exercised at 75% of their maximal capacity, endorphins increased 1.5 times. That’s 150%! When they exercise at 95% of their maximal capacity, endorphins increased 4.4 times.
  • The lesson: that feel-good sensation you get from exercise has to be earned. You earn it with sufficient intensity.
  • After prolonged endurance exercise, cortisol returns to normal in 18-24 hours.
  • When you start exercising with low blood sugar levels (at 3.3 mmol/l or lower), it results in greater cortisol levels.
  • Fasting increases growth hormone, but decreases IGF-1 (insulin-like growth factor 1).
  • Obesity and PCOS (polycystic ovarian syndrome) reduces the growth hormone in response to exercise.
  • There is a strong relationship between VO2max and IGF-1 levels. In other words, the greater your aerobic capacity, the greater your IGF-1 levels.
  • Both a fast and a slow thyroid cause reductions in exercise tolerance, but for different reasons:

• With hyperthyroidism (fast thyroid), there is increased blood flow to muscles, which causes hyperthermia (overheating)
• With hyperthyroidism, there is also a tendency towards tachycardia (fast heart rate).
• With hypothyroidism (slow thyroid), there’s a decreased heart rate, and less delivery of blood to muscles
• Testosterone in men does increase in response to strength training lasting under an hour. But it doesn’t have much of an effect on chronic levels. Testosterone levels are only elevated for a short period of time, before returning to baseline.
• Testosterone levels are lower in endurance trained men compared to untrained men.
• When you sweat, you lose a lot more sodium than potassium.
  • You lose 20-135 mmol/l of sodium, but only 3-35 mmol/l of potassium
    • The variation is this wide, because these losses depend on level of the person training, degree of heat acclimatization and duration of exercise.
• In one experiment, 100 diabetic men were divided into 2 groups: diet only; diet and exercise. At the end of the experiment, both groups showed improvements in oral glucose tolerance, but only the diet + exercise groups showed decreased insulin levels.
• Excessive exercise, which leads to decreased estrogen and progesterone levels in women will also lower bone mass.
• In one study, where women strength trained using 7 repetitions with heavier weights, they increased their bone mass a lot more than women who strength trained using 21 repetitions with lighter weights.
• Impact is key to gaining bone mass. In one experiment, participants jumped 33 times per day for 6 months. Their bone mass at the thigh bone increased 3.4% over that time period. Although interestingly enough, bone mass at the spine did not increase.
• During the luteal phase, which is dominated by progesterone, women’s performance tends to be lower. They are weaker, and tend to have less endurance, compared to the follicular phase, which is dominated by estrogen.
  • Women on oral contraceptives (birth control) don’t experience this variation in strength and endurance.
• A significant increase in cortisol requires at least 20 minutes at 60% of the maximal aerobic capacity (that’s around 70% of the maximal heart rate).
• The best athletic performances tend to be in the evenings. In the last 50 years, the only track and field records that were broken before noon were one in the men’s shot put, and one in the women’s javelin. And that’s it.
• Your digestive system works 50% slower at 8PM, compared to 8AM.

 

As geeky and dense as these points are, I only shared the points that I thought would be easiest to understand. I took 14 pages of notes on Sports Endocrinology, and I look forward to implementing this knowledge with our clients.