Variability in athletic performance

Question 1

Factors that contribute to athletic perf

Answer 1

Genetics:
- chronotype
physical characteristics
- maximal power
- running economy
- VO2max, LT
- flexibility, agility, speed
- thermal tolerance
= muscle fatigue + muscle damage
Circadian Factors
- circadian variation of core body temp
- circadian variation of cortisol

Question 2

How physiological rhythms interact + its impact on perf

Answer 2

• Plasma melatonin = peaks during the sleep period = melatonin induces + maintains your sleep
• Sleep in bright light = impacts sleep = may continue to sleep but may be less deep = experience NREM stages 1 + 2 but maybe not stage 3 = deep sleep
• Temp curve goes in the opposite direction to melatonin = at night body temp goes to its lowest + then comes back up in the second half of the night
• Sleep propensity follows melatonin = depends on activity = in the waking period some people train

Question 3

Endogenous factors affecting individual variation in perf

Answer 3

1. Genetics
   a. Genetic predisposition for certain physical abilities
   b. Anthropometric traits
   c. Chronotype
2. Physiology = physiology is trainable
   a. Muscle composition = e.g. resistance training improves muscle strength/mass
   b. Lung capacity = endurance training improves lung capacity
   c. Cardiovascular health/ fitness
3. Psychological factors = genetics come in to this as well
   a. Motivation
   b. Self-efficacy
   c. Mindset
4. Experience + training

Question 4

Exogenous factors affecting individual variation in perf

Answer 4

1. Environmental conditions = especially if comp occurs outside
   a. Temp, humidity, altitude, wind = can train oneself to deal w/ certain conditions i.e. very hot or cold climatic conditions
2. Nutrition + hydration
   a. Well-balanced diet
   b. Proper hydration
3. Sleep
   a. Duration + quality (melatonin)
4. Coaching + training = important as a coach can help you w/ techniques, training schedules, training strategies + also is also a very important support base + motivator
   a. High-quality training program
   b. Training status
   c. Time of day specific training
   
   5. Competition + social support
      a. e.g., while competing against strong opponents

Question 5

Chronotype + sports performance

Answer 5

Theoretical considerations:
* Endurance
○ M-type perform better in endurance activities
§ Natural circadian rhythm timing being aligned w/ typical comp time
* Strength/ power
○ E-type have an advantage
§ Body temp + muscle strength peaking later in the day
* Injury risk
○ E-type higher risk of injury
§ Less prepared for morning training = still sleepy + groggy in the morning/ comp due to natural circ rhythms

Question 6

Differences in performance between chronotypes
Time of day factors impacting performance:

Answer 6

Time of day factors impacting performance:
1. Circadian variation in core temp
2. Circadian variation in melatonin
3. Circadian variation in cortisol

Question 7

Proposed factors for time of day performance effects (CBT)

Answer 7

• Core body temp (peak PM)
  ○ Higher alertness = than compared to when very low in the middle of the night
  ○ Higher carb utilisation
  ○ Actin-myosin crossbridge cycle in muscle unit = muscle contraction = more efficient

Question 8

Proposed factors for time of day performance effects (cortisol)

Answer 8

• Cortisol (peak AM - immediately after waking = after an hr or so drops back down)
  ○ Two effects:
  § Metabolic (mobilization of glucose, free fatty acids + amino acids) = during exercise cortisol is raised to mobilise fuel sources for energy
  § Cognition = makes you physiologically more aroused = more alert in morning
  ○ Physiological arousal:
  § Low-moderate level – favours perf
  § High level – thwarts perf
  § In terms of perf = cortisol can have a bell-curve shape = don’t want to have cortisol right at the peak when exercising or competing = want it at low to moderate level as it favours perf as cortisol is one of those flight or fight responses

Question 9

Proposed factors for time of day performance effects (melatonin + others)

Answer 9

• Melatonin
  ○ Duration + quality
• Others:
  ○ Training status
  ○ Time of day-specific training

Question 10

Chronotype + core temperature
1. Circadian variation in core temp

Answer 10

• Notice that for core temp = morning types min core temp (nadir) occurs at 5:00am ish for this group, for the evening type of this study = occurs around 7:30am = morning type min core temp is advanced or occurs earlier whereas is delayed or occurring at a later time for evening types
• Happens the same for all other parameters i.e. melatonin, sleep propensity
• If wake up in the night after melatonin peak (when melatonin levels are coming down = can be more awake) + when core temp is starting to rise (also makes you a bit more alert) = unable to fall back asleep = what do you do? = can be productive + do work until tired/ mentally tired
• Phase advance of core body temp in morning type.

Question 11

Chronotype + melatonin
2. Circadian variation in melatonin

Answer 11

○ Late type compared to Early type:
§ late bedtime + rise time
§ delayed DLMO
- For morning type = angle of entrainment (difference) is much longer compared to the evening type
–> the entrainment status suggests circadian misalignment as seen in the phase angle of entrainment (dif in the timing of DLMO + mid-sleep).

• Phase advance of melatonin in morning type

Question 12

Chronotype & cortisol
3. Circadian variation in cortisol

Answer 12

○ Late type compared to Early type:
§ lower cortisol concentrations in the first hr after awakening + therefore demonstrates lower morning arousal
§ Cortisol rhythm - lower cortisol amplitude + later acrophase (the timing of the cortisol peak) –> better cognitive effects PM
§ The amplitude of cortisol is a lot higher in morning types say at 7:00am = tells us physiologically more aroused for the morning type
§ Nadir for cortisol in morning type = occurs around 10:00pm, whereas is at around midnight for evening types = timing of cortisol is different

• Phase advance of cortisol in morning type

Question 13

In considering chronotype
Assess variation in performance as a function of time since entrained awakening – Why?

Answer 13

• Rationale Subjective alertness + perf efficiency determined by:
  ○ a homeostatic process (prior waking) +
  ○ an input from the circadian timing system
• “Time since entrained awakening” (Facer-Childs + Brandstaetter, 2015) = the timing of peak perf, looking at the amount of time since waking up
  ○ LCT: personal best time at ~12h since awakening
  § Should they be expected to be sleepy at that time?
  § Should they be expected to perform their worst?
  § How do you explain this? Slow build-up in sleep pressure in LCT
  ** Performance affected by multiple endogenous factors
  LCT = late chronotype, MCT = morning chronotype
  ○ MCT: personal best time at ~6h since awakening

Question 14

Why are LCT not tired 12hrs after awakening ?

Answer 14

Why are they not tired 12hrs after awakening
* We know that, the duration of prior waking will determine how sleepy you are, the longer you’ve been awake the more sleepy you are = but for these late types, even after 12hrs since awakening = no problem
* Reason is = you don’t accumulate sufficient sleep pressure, whereas for the morning type, they accumulate sleep pressure very quickly + that’s why by 9:00pm they are very sleepy = sleep pressure is intense
* Reason for it = slow build-up in sleep pressure in the late chronotype

Question 15

Not considering chronotype
Time of day variation in sports performance

Answer 15

Without consideration of circadian phenotype, athletes appear to perform their personal best in the evening = around 4-6pm

Question 16

Time of day variation in sports performance
* Chronotypes

Answer 16

○ ECT (n=5): personal best time at ~6h since awakening
○ LCT (n=5): personal best time at ~12h since awakening
○ + Chronotypes differ in perf time when examined according to the time since entrained awakening
○ + * Timing of tests not randomised
○ Limitations: only 5 people in the early type testing + 5 in late type testing, also looked at MEQ instead of MCTQ

Question 17

Performance at circadian peak

Answer 17

Performance is better during games occurring close to their circadian peak in perf (1) Smith et al., 2013
* the WC teams beat the point spread about twice as often as EC teams i.e., a strong adv for WC teams over EC teams even accounting for the point spread –> players playing close to the circadian peak in perf (?) demonstrate a significant athletic adv over those who are playing at other times

○ Were there other factors that might have influenced perf? = didn’t assess every player in the teams = don’t have a lot of info about indiv players within teams = + whether they had good sleep recovery, whether their nutrition is good, whether they were hydrated, the ambient conditions etc…
* Circadian phase not defined - no measure of polysomnography or temp/melatonin rhythms (time zone dif, crowd effect a home field adv?
* Caffeine intake/ use of perf enhancing substances not measured
* The point spread (from dif sources) can change over time depending on gambling behaviors = they can use any info for the point spread = therefore there is no consistency in the way this data has been presented
* Not known if the losing teams had a reduction in motivation, endurance, strength, reaction time, flexibility +/or cognitive perf

Question 18

Time of day variation strongly affects perf in Olympic athletes (Lok et al, 2020, University of Groningen, the Netherlands) - swimming

Answer 18

• Race types:
  ○ heat, semi-final, + final per indiv for each stroke, distance + Olympic venue
• Swim perf was better during finals as compared to semi-finals + heats –> highly motivated!
  ○ Swimming time was best for finals = however these could be due to time of day effects
• Could the findings be explained by time of day effects?
  
  • Perf showed fastest swim times in the late afternoon = dependent on time of day
  • Physical perf determined by:
    ○ training +
    ○ the endogenous circadian system

Time of day on all-out swimming (Baxter & Reilly, 1983)
* Improvement across the day:
○ 3.5% for 100 m
○ 2.5% for 400 m
§ At the afternoon times = there perf was much better than the morning
* Perf strongly related to increased oral temperature in the afternoon
○ The higher the body temp = the better the perf

Question 19

Time of day effect on self-chosen work-rate and rectal temperature

Answer 19

• PM exercise: higher work-rates initially chosen, then ↓ w/ ↑ temp creep = as the day progresses, their ability to do higher work rate declined
• AM exercise: lower work-rates initially, then ↑ w/ a slower temp creep
  ○ How to explain these results = core body temp = because temp is higher than morning when they first started the exercises = they were able to achieve a higher work rate = but their work rate gradually went down because of their high temp
  ○ Exercises that occur in the morning = temp was low = therefore selected lower work rate = of course temp caught up, similar to that for the afternoon group + therefore their exercises were sustained
• Perf in sustained exercise is improved by lower body temps

Question 20

Psychological factors

Answer 20

• Perception of effort (RPE scale)
  ○ the greatest RPE occurs in the afternoon –> a lower perf
• Factors for consideration:
  ○ ‘vitality’ on the POMS (Profile of mood state) scale higher PM (higher workload/ power achieved PM)
  ○ motivational factor of comp
  ○ pain resulting from injuries/ discomfort due to extreme exertion
• Note: greater pain tolerance/ discomfort early AM

Question 21

Cognitive performance rhythms

Answer 21

• Cognitive ability
  ○ focus, visual attention, visual tracking + fast decision-making
  § These are affected by chronotype e.g. if you work best in the morning due to being an early type = you tend to be more alert + you tend to think more clearly + also make more decisive plans + decisions
  § Circadian timing can affect your cognitive abilities
• Cognitive perf rhythms
  ○ peak in the late afternoon
  ○ affect athletic perf involving:
  § Strategy
  § decision-making
  § recall of complex coaching instructions during comp