Variability in athletic performance 2

Question 1

Exercise guidelines incorporate:

Answer 1

• Volume
• Frequency
• Intensity = by far most important to induce training adaptations
• But not timing of exercise.
  Why?

Question 2

What is chrono-exercise about?

Answer 2

1. Reset (phase shift) the master body clock
   a. Exposed to morning light = will advance bedtime
   i. Reason we need to be daily exposed to morning light = mainly because the body clock is slightly longer than 24hrs for most people = will reset clock
   b. Exposed to afternoon sun = delay bedtime
   i. Older adults tend to go to bed too early so afternoon sun exposure is good
2. About devising exercise timing based on circadian rhythms
   • Exercise + energy metabolism
     ○ Hormones that are involved in energy metabolism exhibit circadian rhythms, e.g.,
     § Insulin: Glucose intolerance lower in evening than in morning
     ∴ need consider exercise timing

Question 3

Exercise/ food intake

Answer 3

• The SCN synchronises peripheral clocks to create a coordinated circadian rhythm of metabolic processes
• SCN = coordinating peripheral clocks = Means that during exercise = all the metabolic processes are coordinated appropriately = SO IMPORTANT
• Can see = during sleep period = there is decreased insulin secretion = therefore should you consume a meal or exercise during the sleep period = will find that insulin secretion is inadequate = therefore leading to glucose intolerance
• Cholesterol synthesis = occurs during sleep period + obviously when sleeping consume less energy

Question 4

changes in metabolism-related indicators in exercise timing

Answer 4

• There is a circadian timing of their appearance + concentration
• IL-6 = cytokine naturally released during exercise = it increases glucose uptake, increases FA metabolism,
• GH = when people deficient in this hormone = grow a lot of visceral fat as GH is not there to regulate the adipose tissue volume
• Catecholamines = noradrenaline, adrenaline
• Corticosterone = cortisol
• SCFAs = short chain FA
  –> Evening exercise most effective in promoting high rates of lipolysis

Question 5

How can you take advantage of the fact that evening exercise promotes high rates of lipolysis? Consider mode and intensity of exercise

Answer 5

• Perform endurance exercise at PM
  ○ At ~40-65% VO2max: FA oxidation
  ○ At 65% of VO2max:
  § ↓ FA contribution
  § ↑ intramuscular TG mobilization
  ○ Above ~80% of VO2max:
  § carb main energy source (Muscella et al, 2020)
• Perform resistance exercise at PM
  ○ uses fat as an energy source (Muscella et al, 2020)
• Increase fat utilisation will lead to carb sparing = why would want to have carb sparing = have lots of reserves of fat/ storage = whereas carbs stored are less + when deplete these = hit a wall = no more carb to use as energy = experience muscle fatigue

Question 6

Improved lipolysis and weight loss

Answer 6

• Take adv of evening exercises that favour lipolysis
• Exercise training
  ○ ↑ FA mobilization
  ○ ↑ the exercise intensity which prompts a higher rate of lipolysis
• Exercise in fasting state/ after high protein breakfast
  ○ ↑ FA oxidation in healthy subjects
• Resistance training/high-intensity endurance training
  ○ Gain in muscle mass –> ↑ basal metabolic rate –> ↑ energy expenditure + caloric restriction
• • caloric restriction = to lose weight

Question 7

HEART RATE
Time of day variation in exercise heart rate

Answer 7

• Exercise HR exhibits circadian variation
• Exercise HR
  ○ lowest at ~4am = during sleep period
  ○ highest at ~6pm = when you exercise at the same work intensity = the HR is highest at 6pm compared to during the sleep period or at midnight
• Application: PWC170
  ○ a submax test for predicting VO2max
  ○ has a large predictive error in part due to the time-of-day at which the test was administered
• PWC170 – physical work capacity at target heart rate of 170
• This figure tells us there is a circadian variation in HR = PEAKING at around 6 in the afternoon, lowest during the night at around 4:00am

Question 8

Time of day variation in VO2max

Answer 8

Time of day variation in VO2max
Time of day variation
* Significant differences: 5 studies
* Different findings in sub-groups: 3 studies
* No significant differences: 7 studies

Inconsistent findings –>
* Measurements at 2-time points only
* Sequence of investigated times of day (no randomisation)
* Did not consider exhaustion criteria at VO2max
* Chronotype not considered
* Habitual training time not considered

Question 9

Time of day-to-day variations in VO2max

Answer 9

Time of day-to-day variations in VO2max
* Mean dif in VO2max = 2.0 ± 1.0 ml/kg/min
* Why is it important to be aware of the day-to-day variations?
○ Example,
○ Training program: VO2max improved
○ But need show an increase in VO2max greater than the normal day-to-day variation of 2 ml/kg/min
○ Daily fluctuations must be taken into consideration

Question 10

VO2max
Time-of-day variations in VO2max

Answer 10

VO2max
Time-of-day variations in VO2max
- VO2max between the different times of day
* Not significantly different
○ –> Peak VO2max was achieved at different times of the day by different athletes
○ –> masks the time of day effect

Question 11

Diurnal variations in VO2max

Answer 11

• There is a diurnal variation in VO2max
• The mean dif of 5 exceeds day to day variation of 2 = the results are valid
• Majority of athletes had their peak in the afternoon
• A significant peak-to-trough (diurnal) dif in VO2max of 5 ml/kg/min
• Peak VO2max occurred at 4-7pm
• Diurnal variation in VO2max is 2.5x greater than the day-to-day variation

Question 12

Percentage of participants reaching their best VO2max (ml/kg/min) at 4pm or 7pm for early and late chronotype

Answer 12

• Early chronotypes did not reach peak perf earlier during the day
• Late chronotypes did not reach it later during the day

○ –> data contradicted findings of Facer-Childs + Brandstaetter (2015) ⇒ MEQ rather than MCTQ (MEQ only tells of preferences for bedtime + rise time whereas MCTQ tells you about the timing of your sleep + waking which is more in line w/ your genetic trait); small sample size; not randomised; *perf time since entrained waking

Question 13

VE, VCO2, CBT

Answer 13

• VE + VCO2 reach circadian nadir (min) ~6-8h earlier than the CBT nadir
• VE not in phase w/ CBT pattern
• A close temporal r/s b/w VE, VO2 + VCO2
• CO2 produced drives VE = so when track changes in VE across the day = will find that VE + VCO2 track one another = always in the same waveform as CO2 drives breathing
• Hyperventilate = CO2 is reduced = VE reduced because there isn’t enough CO2 drive to drive your breathing
• CO2 is a basic stimulus for your breathing
• CBT = double plot as repeating measurement = high during the day, low at night
• VCO2 = fairly low during the night = drops off as go to bed, starts to rise as you wake in the morning due to different activities that you perform = VE fluctuates during the day but eventually comes down to the lowest level when start to go to bed

Question 14

Time of day specific training
What are maximal short-term exercises?

Answer 14

What are maximal short-term exercises?
* Maximal exercises of duration < 1 min
* Comprise both exercise modes: endurance + resistance, e.g.,
○ all-out sprints, maximal jumps, isometric contractions
○ involve anaerobic metabolism
* Depend on peripheral AND central mechanisms of muscle contraction
○ central mechanisms: CNS, central command (central output from the motor region of the brain that goes to your skeletal muscles), alertness + motivation = if not highly motivated perf mightn’t be as good
* A robust model to explore time-of-day effects on the musculoskeletal system

Question 15

Maximal short-term exercises exhibit diurnal fluctuations: peaking between 16:00 and 20:00 h

Answer 15

Can training at a specific time-of-day reduce diurnal variations of max short-term exercise performance?

• At baseline: Wingate test, SJ, CMJ, and MVC (maximal voluntary contractions) significantly higher in the evening (1700– 1800 h) compared to the morning group (0700–0800 h)
  ○ –> diurnal variation
  ○ Explanations: higher core body temp, faster VO2 kinetics (the rate of rise of a reaction/any variable –> looking at behaviour of O2 uptake from rest to exercise) = say VO2 kinetics is faster in the afternoon then the morning
• Following training: Significant increases in anaerobic perfs in both groups (similar magnitude of gains after training + tapering) at the time of day at which training was conducted

Question 16

How did 12 weeks of resistance training affect the diurnal variation in maximal short-term exercise performance?

Answer 16

• Diurnal variations:
  ○ Blunted in the MTG = less diurnal variation
  ○ Persisted in the ETG + CG

Question 17

MVC of knee extensors – AM vs PM

Answer 17

• Morning training group (MTG)
  ○ Significant improvements seen in the AM session only
  ○ Decrease in diurnal variation in the MTG
• Evening training group (ETG)
  ○ Significant improvements seen in the PM session only
  ○ Diurnal variation persisted in the ETG
• Notice that after training the MVC = the difference is less = means the circadian variation is reduced, + tapering is also further reduced

Question 18

Better short-duration maximal exercise performances were achieved between 16:00 and 20:00 h compared with the morning (Practical application Mirizio et al, 2020)

Time-of-day deleterious effects minimized after:

Answer 18

Time-of-day deleterious effects minimized after:
* A 10-min warm-up period while listening to neutral or self-selected high-tempo music (>120–140 bpm) through headphones
* A 60-min exposure to warm + humid climate conditions (28.1– 29.5 °C, 62.6–74% relative humidity)
* Active warm-up protocols (e.g. 12–15 min pedalling at min intensities of 50% VO2max + interspersed w/ 5-s sprint exercises)
* 2-4 weeks of intermittent fasting conditions of 15–16 h starvation/day from ≈04:00 h till ≈19:00 h
* A training period of at least 5 weeks performed in the morning

Question 19

Flexibility

Answer 19

Fingertip to floor:
* Trough at AM
* Maximum midday to midnight

Trunk flexibility:
* Trough at AM
* Peak at PM = showed that max flexibility occurred in the arvo

Question 20

Time-dependent changes in human stature
* in the context of injury and rehabilitation

Answer 20

• Lose 50% of height in the first hr alone, within 3 hrs lose 80%
• Means in afternoon don’t lose much height as discs already compressed = more stiff in the arvo

Loss in height
* Day: weight bearing in upright posture – vertebral disc compression
* Night: recovery
○ –> day-night cycle of activity + rest
* Lose a couple of cm during the day = approx 1.1% of height
* What can cause shrinkage = gravity acting on your vertebral column

• Stature losses were smaller in the evening when body height is in the trough of circadian variation
• Greater stiffness of intervertebral discs in the evening –> increase risk of injury
• Higher values of back strength in the evening may serve to compensate for the increase in stiffness