Variability in athletic performance 2 Flashcards
Exercise guidelines incorporate:
- Volume
- Frequency
- Intensity = by far most important to induce training adaptations
- But not timing of exercise.
Why?
What is chrono-exercise about?
- 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 - 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
- Exercise + energy metabolism
Exercise/ food intake
- 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
changes in metabolism-related indicators in exercise timing
- 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
How can you take advantage of the fact that evening exercise promotes high rates of lipolysis? Consider mode and intensity of exercise
- 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
Improved lipolysis and weight loss
- 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
HEART RATE
Time of day variation in exercise heart rate
- 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
Time of day variation in VO2max
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
Time of day-to-day variations in VO2max
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
VO2max
Time-of-day variations in VO2max
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
Diurnal variations in VO2max
- 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
Percentage of participants reaching their best VO2max (ml/kg/min) at 4pm or 7pm for early and late chronotype
- 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
VE, VCO2, CBT
- 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
Time of day specific training
What are maximal short-term exercises?
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
Maximal short-term exercises exhibit diurnal fluctuations: peaking between 16:00 and 20:00 h
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
How did 12 weeks of resistance training affect the diurnal variation in maximal short-term exercise performance?
- Diurnal variations:
○ Blunted in the MTG = less diurnal variation
○ Persisted in the ETG + CG
MVC of knee extensors – AM vs PM
- 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
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:
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
Flexibility
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
Time-dependent changes in human stature
* in the context of injury and rehabilitation
- 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
