Module 4 - Measuring energy usage & exercise intensity

• Exercise intensity gives indication of:

  • Sustainability of exercise
  • in training, performance, fitness testing
  • Safety of exercise
  • in sedentary people or clinical populations
  • Management of disease
  • how respond to treatment or recovery
  • Nature & magnitude of stimulus for adaptation
  • frequency & type
  • pros & cons
• Absolute exercise intensity of ‘categories’ can differ enormously bw/ people

  • As have different resting HR (& therefore RPE)
  • Different VO2 max
• Objective measures of intensity include:

  • METs
  • HR max
  • HRR (Heart Rate Relative/Recovery)
  • VO2 max
• RPE is a subjective measure of intensity
• Descriptive measures of intensity include:

  • Description of intensity
  • Talk test
• People are different so intensity varies bw/ people
• "Smart" devices are not valid indicators of intensity
• Common ways to describe & measure intensity:

  • Physical:
  • Speed
  • Power output
  • Force
  • Physiological:
  • Measuring oxygen consumption given % VO2 max
  • If want to look at relative use mL/min/kg (very linear)
  • Lactate - look anaerobic
  • Psychophysical:
  • RPE
• RPE may be as valid as physiological techniques (correlated with HR)
• Ventilatory Thresholds:

  1. VT1 = prolonged/steady state exercise
  2. VT2 = severe/maximal exercise

  • Useful indicator of ventilatory efficiency
• Anaerobic threshold (usually refer to 2nd one) = increase ventilation & lactate

  • Threshold can be extremely hard to identify & to interpret, esp for lactate
• People differ greatly in ability to sustain exercise at given [Lactate]
• RER = Respiratory Exchange Ratio

  • = VCO2 / VO2
  • 1st increase indicates VT1
  • RER > 1.00 indicates increase (anaerobic) glycolysis
• • METs = Activity Met Rate / Resting Met Rate (RMR)
  • 1 MET = RMR ~3.5 mL/O2/min/kg
  • Mainly used in health & PA contexts
• HR used in 3 ways to indicate intensity:

  1. Different ages have different HR max (HR max = 220 - age)
  2. Relative to max: %HR max =HR / HR max * 100
  3. Relative to available range: %HRR = (HR - HR rest) / (HR max - HR rest) * 100
  4. Excellent indicator of exertion
• Trained into account as training have a lower resting HR (& HRR)
• Linear relationship between HR and O2 consumption
• • HR shows no thresholds
  • So, HR used as intensity marker partly just based on representing other factors, eg metabolic state
• Economy = Energy expended to maintain constant speed or per unit distance travelled

  • (~1 kcal.kg-1.km-1)
  • on avg related to mass
  • When can measure work output
• Efficiency = Metabolic cost of work: work conducted / energy expended * 100 (%) (gross efficiency)

  • Typically what we measure
  • Gross & Net efficiency both useful
  • Net efficiency = work / (energy expended-BMR) * 100
  • Only possible if know work, so economy is a more versatile measure than efficiency is
• Factors that influence economy & efficiency:

  • Bike set up
  • Stride length, cadence in running (is an optimal)
  • Frequency can affect cadence & economy too
  • Speed of movement (walking)
  • Fibre composition of muscle
  • Higher efficiency in muscle with greater amount of slow twitch fibres
  • Training status, experience, age
  • Posture & familiarity with activity or ergometer
• Higher efficiency with more type 1 (slow twitch/aerobic) fibres
• Some measures linear others not, linear ones can be used to predict (eg VO2 from HR; Vo2 max from submax test)
• • Economy: VO2 / distance or speed (when work output difficult to measure eg running)
  • Efficiency: work / EE used (%)
• Direct calorimetry is measure of heat to determine energy use (EE)
• Indirect calorimetry is measure of respiratory gas exchange (VO2 in, VCO2 out) to measure EE

  • Can use just O2, but less accurate
• RER (VCO2/VO2) gives substrate oxidation:

  • RER = 0.7 = 100% Fat,
  • RER = 1.0 = 100% CHO
  • RER = 0.85 = 50/50
  • RER to relate to RQ utilisation & production of gases at cellular level
• RER > 1.0 anaerobic metabolism, can no longer use to determine substrate mix, amounts & EE
• Absolute rate of fat oxidation (g/min) is not necessarily greatest (Fat max) at intensity w/ greatest E% fat oxidised

  • Absolute rate of fat oxidation is that intensity w/ fat being oxidised
• Can use HR (or work rate) to estimate EE; best if have done test in which both measures to determine relationship, for that exercise mode
• Use more energy if fit, intense, long, high BM, inefficient
• Aerobic power is a function of bodies systems (pulmonary, CVS, nervous, musculoskeletal)

  • Also correlated w/ longevity
• Energy cost of given workload:

  • Efficiency & economy (eg equipment & technique)
• Most energy is lost as heat
• 2/3 of energy lost as heat just to make ATP oxidatively

  • So, work rate usually <25% of metabolic rate
  • Can measure energy usage only in steady state
• Can only measure energy usage during steady state exercise

  • To get good measure of energy utilisation
• For non-steady state exercise measure energy expenditure over a long enough duration (to get avg)
• Best to worse ways to measure total daily EE:

  • Doubly labelled water
  • Accelerometers (HR or GPS)
  • Heart Rate (HR)
  • Accelerometers
  • Pedometers
  • Activity log
  • Activity recall + BMI
  • Activity recall
• Best to worse ways to measure EE in activity:

  • VCO2 & VO2
  • VO2
  • Work rate of HR
  • Walking/running speed without knowing body mass
• Calorimetry:

  • = The measurement of metabolic energy transformation (metabolic rate)
  • = Heat production if no net mechanical energy production
  • Work rate (measurable using ergometers or estimations)