Exercise intensity assessment and interpretation

Question 1

Exercise intensity: definition?

Answer 1

• Refers to the physiological response to a given external work rate
• External work rate itself is not the intensity of exercise

• Normalising exercise intensity is the attempt to ensure all
participants experience an equivalent physiological demand

Question 2

Ensuring a comparable exercise intensity is important, why?

Answer 2

• Ensuring a comparable exercise intensity is important:

• For studies designed to measure the physiological or psychosocial
impact of an intervention or stimuli

• For the design of effective training or rehabilitation programmes

Question 3

Why account for exercise intensity?

Answer 3

• Metabolic, gas exchange, and perceptual responses vary greatly at different intensities
• Intra and inter individual variability obscures real differences

Question 4

what underpins the variance in response?

Answer 4

• Submaximal thresholds
• Lactate or gas exchange threshold
• Maximum lactate steady state

Question 5

Prescribing exercise intensity as a percentage of VO2max is widely used, why?

Answer 5

• Better than using just external work rate

• Relies on a valid VO2max and fails to account for the
variation in the occurrence of submaximal thresholds:

• Lactate threshold varies widely between people, can
occur between 30 – 85% VO2max

• Physiological and perceptual responses very different
above and below the GET and MSS

Question 6

Same % VO2max, Same Intensity?

Answer 6

• Main difference is one participant’s VO2 reaches a
steady state, whilst the other’s keeps rising

• Indicative of exercise being much more difficult for the second participant

• In a test to exhaustion at this ‘same’ intensity, 1
participant would last >4hrs, the other would last
~10-20 minutes

Question 7

Exercise intensity Domains?

Answer 7

• It is accepted that there are 4 exercise intensity domains (Burnley and Jones, 2007):
• Moderate, Heavy, Severe, Extreme
• Knowledge of these domains is critical for understanding differences in the physiological response to exercise

Question 8

Exercise intensity domains: domain threshold?

Answer 8

• Moderate – below the LT
• Heavy – above LT, below MSS
• Severe – above MSS achieving VO2max
• Extreme – exhaustion before VO2max

Question 9

Vo2 slow component?

Answer 9

• A slowly developing component of VO2
that becomes evident
after 2-3 mins

• Only seen above the LT (i.e. never during moderate intensity exercise)
• Eventually levels off during heavy intensity exercise

Question 10

Most likely explanation of the slow component?

Answer 10

• Additional motor unit recruitment:

* The original hypothesis was that additional fibres were recruited to replace fatiguing fibres

Question 11

How to calculate cycling economy or Gain?

Answer 11

Change in Vo2/change in work load

Question 12

Moderate intensity exercise:

Answer 12

• All exercise below the LT with no elevation in blood lactate

• VO2
increases at ~10 ml·min-1
·W-1

• All team sports involve periods of moderate intensity exercise
• Rare in other top class sports
• Recreational runners will commonly exercise in the moderate domain
• Moderate exercise can be continued for ~4hrs
• Fatigue is likely related to muscle glycogen depletion, muscle damage, and/or increased core temperature

Question 13

Heavy intensity exercise?

Answer 13

• All work rates that are above the LT below the MSS where a steady state in VO2 will eventually be attained
• Differs significantly from moderate
• Closer heavy exercise is to the LT = smaller the VO2 SC

• Crucially – even if exercise is completed to exhaustion, VO2
remains sub-maximal – i.e. a steady state will be attained

• VO2
‘gain’ may reach ~12 ml·min-1
·W-1 due to the VO2 SC

Question 14

Heavy Intensity Exercise and Sport?

Answer 14

• HR – delayed, elevated steady state attained
• Bla – elevated above baseline but a steady state will be attained
• Many endurance events (including the marathon) are performed predominantly within the heavy domain
• Constant work rate activities lasting ~30 - 120mins
• Fatigue is complicated
• Combination of metabolite accumulation and substrate availability

Question 15

Severe intensity exercise?

Answer 15

• All work-rates that are above the maximum steady state where
VO2 max is attained if exercise is continued to exhaustion

• It is the VO2 SC that causes VO2
to reach its maximum

• A steady state will never be reached during severe exercise

• HR – No steady state will be achieved; HR will continue to rise
until HR max is achieved

• BLa – no steady state; will continue to rise until exhaustion

Question 16

Severe Intensity Exercise? Exercise in the severe domain is unique for 2 reasons:

Answer 16

1. It encompasses a wide range of work rates which
   results in the attainments of VO2max
2. Exercise tolerance is significantly limited, but also predictable

• Finite amount of work can be done above MSS,
thus exhaustion can be estimated with remarkable accuracy

Question 17

Severe intensity exercise and sport?

Answer 17

• 1,500 – 10,000m track events are conducted largely in the severe
domain

• Durations of 2 - ~30 minutes
• Getting pacing wrong can have dire consequences

• There is no recovery if work rate is reduced but stays in the
severe domain

• Fatigue is related to PCr depletion and accumulation of fatiguing
metabolites (Pi, H+).

Question 18

Extreme intensity exercise?

Answer 18

• Work rates that are so high that fatigue ensues before VO2 max has been attained
• The highest defined exercise intensity domain
• Time to exhaustion usually <90s
• Fatigue mechanisms similar to severe (PCr depletion and accumulation of fatiguing metabolites)
• Relatively little work has been done in this area
• HR – No steady state will be achieved; exercise will cease before HR max is attained
• BLa – No steady state; value may be surprisingly low due to short duration of exercise