Chapter 6 - Energy Balance and Availability Flashcards
energy balance
balance between energy expenditure and energy intake
For the athlete, even short-term variations in energy balance (and, thus, in body mass) can have a dramatic impact on performance
metabolizable energy
differences between the absolute energy of ingested food and any energy lost in feces and urine
The metabolizable energy of each macronutrient is approximately:
* 4 kcal/g for carbohydrate
* 4 kcal/g for protein
* 9 kcal/g for fat
* 7 kcal/g for alcohol
thermic effect of alcohol
7 kcal/gram
direct vs. indirect calorimetry
direct: necessitates use of a process called direct calorimetry and highly controlled lab conditions
indirect: the type and rate of substrate utilization are measured from gas exchange measurements (carbon dioxide production and oxygen consumption) during both rest and steady state exercise
examples of CSNC-available calorimetry estimate equations
- Harris Benedict
- Mifflin-St. Jeor
- Activity Factors (AF) (Multiply BMR x AF to get Estimated Energy Requirements (EER)
Little to no exercise: EER = BMR x 1.2 (for in bed); for out of bed but low activity, use 1.3
**Light exercise **(1–3 days/week): BMR x 1.375
Moderate exercise (3–5 days/week): BMR x 1.55
Heavy exercise (6–7 days/week): BMR x 1.725
Very heavy exercise (e.g., 2 workouts/day; intense workouts or athletic training): EER = BMR x 1.9
components of energy expenditure
- BMR (RMR) (60-70% of TDEE for basic physiological functions)
- excercise activity thermogenesis (~30% for average athletes)
- ** thermic effect of food** (~10% of TDEE)
component of energy expenditure
resting metabolic rate
- largest component of energy expenditure (60-70% of TDEE)
- Different tissues within the body have distinctly different resting energy requirements. For example, organs such as the liver, gut, brain, kidney, and heart have high energy requirements and account for approximately 75% of resting metabolic rate.
Despite skeletal muscle comprising almost 40% of total body weight, muscle has a much lower energy requirement than these vital organs and comprises only 20% of resting metabolic rate
component of energy expenditure
activity thermogenesis
- activity and non-activity thermogenesis
- by far the most variable component of daily energy expenditure
- 30% of total daily energy expenditure and, in some cases, can be as high as 70–80%
energy availability
Energy availability = (Energy intake – exercise energy expenditure) ÷ fat-free mass
example with a cyclist:
Energy intake (8,000 kcal) – exercise energy expenditure (5,600 kcal) / fat-free mass (70 kg)
Energy availability = (8,000 – 5,600) / 70
Energy availability = 2,400 / 70 = 34.3
EA = 34.3
daily energy balance vs daily energy availability
optimal energy availability in athletes
Though optimal levels of energy availability in athletes are not currently known, an energy availability of
1. 45 kcal/kg fat free mass (FFM) per day for females
2. 40 kcal/kg FFM per day for males
provides a threshold to maintain normal physiological function
low energy availability (LEA)
A state in which insufficient energy is available for normal physiological functions
amenorrhea
The absence of menstruation
functional hypothalamic amenorrhea (FHA)
A form of amenorrhea and a chronic absence of ovulation
athletes who compete in weight-sensitive sports and/or sports that require high levels of energy expenditure seem to be at higher risk of LEA. In contrast, LEA is less prevalent in athletes who compete in sports where daily energy requirements are significantly lower and there is less importance placed on overall body size and composition
consequences of LEA
- Disruptions to reproductive function and sex hormone production
- Increased risk of low bone mineral density
- Alterations in metabolic rate
- Reduced psychological well-being
- Reductions in performance
