Energy expenditure and fatigue

ICF Performance Education Webinar Free Online Series

ICF Performance Education: Free online series

Zsuzsanna Kneffel, PhD
Zsuzsanna Kneffel profile picture


Zsuzsanna has completed her PhD in educational and sports sciences, focussing on "left ventricular morphological and functional characteristics in athletes of different level". This followed a masters degree in physical education.

Zsuzsanna has been an associate professor of physical education in Hungary since 2019, following eight years in Qatar. 

She is a well published author and reviewer of journal articles on a variety of topics related to physical health and performance, and has presented on these topics throughout the world including in Qatar, Austria and the USA. 

Zsuzsanna holds many professional memberships including the American College of Sport Medicine and the European College of Sport Science, and is a Board Member for Sports and Exercise Medicine.

Session information

Measuring energy expenditure
  • Direct calorimetry
  • Indirect calorimetry
Energy expenditure at rest and during exercise
  • Basal and resting metabolic rates
    • Key Point: BMR is influenced by fat-free mass, body surface area, age, body temperature, psychological stress, and hormones.
  • Metabolic rate during submaximal exercise
    • Key Point: Exercise intensity determines metabolic rate during exercise.
    • Key Point: Oxygen uptake during exercise consists of slow and fast components.
    • Key Point: VO2 drift refers to the slow increase in oxygen uptake during exercise at a constant workload.
  • Maximal capacity for aerobic exercise
  • Anaerobic effort and exercise capacity
    • Lactate threshold
      • Key Point: Defined as the exercise intensity at which blood lactate begins to rise quickly
      • Key Point: With intense aerobic training, full adaptation of maximal oxygen uptake is generally achieved after 8 to 12 weeks. However, endurance performance can continue to improve despite the lack of further increases in maximal oxygen uptake. This continued performance improvement is most likely due to increases in the lactate threshold.
      • Key Point: The energy required to restore muscle PCr and ATP stores and to clear lactic acid from the system contributes to excess postexercise oxygen consumption. However, additional contributing factors include restoration of myoglobin and hemoglobin oxygen stores, increased cardiovascular and respiratory activity, and elevated body temperature.
  • Energy cost of various activities
    • Key Point: Energy cost of a given activity is influenced by the type of exercise, exercise intensity, exercise duration, age, sex, body weight, and body composition.
Fatigue and its causes
  • Energy systems and fatigue
    • PCr depletion
      • Key Point: PCr and ATP concentrations decline during intense exercise.
    • Glycogen depletion
      • Glycogen depletion in different fiber types
      • Depletion in different muscle groups
      • Glycogen depletion and blood glucose
      • Mechanisms of fatigue with glycogen depletion
  • Metabolic by-products and fatigue
    • Heat, muscle temperature, and fatigue
      • Key Point: High body temperatures impair muscle function and muscle metabolism.
    • Lactic acid, hydrogen ions, and fatigue
  • Neuromuscular fatigue
    • Neural transmission
    • Central nervous system



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