Muscle Damage, Fatigue and Circadian Rhythm Flashcards
1
Q
Circadian Rhythms
A
- Expression representative of 24-hr fluctuations in the following factors:
○ Endogenous (i.e. the “body clock”)
○ Exogenous (i.e. ‘zeitgebers’; such as light-dark cycle) factors
○ Attributed to a mixture of influences from the external env, sleep-wake cycle + an internal “body clock” (i.e. suprachiasmatic nuclei (SCN))
2
Q
Body Temperature
A
- Body temp is a suitable indicator of circadian time
- Body temp higher in evening then morning = temp increases as approach later part of the day
- Souissi et al. [1] showed that oral temp could be used to predict occurrence of maximal + minimal values in the circadian rhythm of anaerobic perf
○ Look at pattern of temp = see its very similar to the exercise perf, so in terms of mean power = see a very similar type of pattern emerge = same w/ peak + max power
3
Q
The more muscle temp decreases the more muscular perf decreases.
A
- Greater increase in vertical jump height w/ increasing muscle temp
- W/ higher temps = the perf of the indiv especially in anaerobic type of task is going to be enhanced
4
Q
Possible reasons for improved anaerobic exercise + muscle strength w/ higher body temp=s
A
- Increase in carb utilisation over fat as a fuel source.
○ Can use w/ or without O2
○ Fat = not ideal for a high intensity bout as fat molecule takes a lot longer to break down + to use that energy - Better facilitation of actin-myosin cross-bridge mechanics within the musculoskeletal unit due to:
○ increase calcium release from sarcoplasmic reticulum.
○ Reduced concentration of inorganic phosphate = by-product of metabolism = causes inhibition of cross-bridge cycling = tends to slow it down + influence amount of Ca2+ released from SR
5
Q
Passive warming
A
- Although, passive warming (i.e. deep heat or heater) to increase core body + skeletal muscle temp did not completely ablate diurnal variation in repeated sprint perf [4].
- Factors, independent of heat, may regulate circadian exercise perf, particularly in regards to power and/or strength.
6
Q
Rating of Perceived Exertion
A
- Conflicting results based on RPE during morning versus afternoon/ evening exercise
- During repeated sprints RPE has been found to be lower in the morning [5], evening [6], or no difference during a Wingate test [7].
- Contradictory results of studies are, perhaps, due to differences in exercise protocols + too few testing times during the day.
○ View of exercise can also be influenced by chronotype, sleep, stress levels, temperature etc - RPE useful in conjunction w/ other tools
- If someone has higher RPE in morning than evening = most likely due to time of day = not adaptative change
7
Q
Effects of circadian rhythm on physical performance and skeletal muscle
A
- Peak short-term maximal perf achieved in afternoon/evening - body temp (amplitudes ranging b/w 3% + 22%).
- How about the circadian effects on muscle fatigue?
8
Q
What is Muscle Fatigue?
A
Many definitions………..
Our definition is:
* The failure to maintain a required or expected power output
○ Reversible w/ rest
* Origins linked to peripheral and/or central mechanisms.
Peripheral fatigue: Biochemical + ionic changes at the muscle level that could alter contractile process +/or excitation-contraction coupling.
Central fatigue: Decline in motoneuronal output +/or central motor command = motivation tied into central fatigue concept
9
Q
Nicolas et al [8] showed that the diurnal variation in torque (maximal voluntary contraction - MVC) decrease defined 2 phases:
A
- 1st to 26th Rep
- 26th to 50th Rep
- Based on EMG results (quads) diurnal variation in muscle fatigue during 50 MVC’s reflected:
* Greater contractile capacity at 18:00 h
* Higher fatigability at 18:00 h = greater drop off in perf (as look at beginning reps, then final reps = change in torque produced from beginning to end compared to morning exercise)
10
Q
Lericollais et al. [9] showed decrement in muscle power during a 60-second Wingate test defined at 2 phases: (i) first 20 seconds, (ii) 21 to 60 seconds
A
- Fatigue index (peak power minus minimal power divided by peak power) higher at 18:00
= higher fatigue index = suggests greater levels of fatigue present - In the first part of the test, there is something that occurs that allows the generation of greater force or greater power output in the evening compared to the morning
- See that sports w/ really short perf = enhanced?
- Continual activity = not much change whether in evening or morning
11
Q
In the study of Souissi et al. [10], power output was examined at evening compared to morning during a 30-second Wingate test.
A
- Phase two: Last 15 seconds - no dif b/w morning + evening.
- Greater decrement in power output found at evening.
- Perf differences due to modifications prevailing at the peripheral rather than central level (based on EMG findings).
12
Q
Chtourou et al. [11] examined repeated sprints performed in the morning versus evening.
A
- Higher power decrement in sprints during evening.
However…….
Other studies have found:
* No differences in Wingate perf in the morning versus evening in trained cyclists [12].
* Greater fatigue in morning than evening during the Wingate test [13].
13
Q
The results (below) from Racinais et al. [14] provides evidence that higher torque and power decrements observed in the afternoon:
A
- Likely a mathematical/statistical consequence of a greater initial torque or power output in the afternoon as compared to morning
○ No greater fatigue in the evening than the morning if we factor in that perf is going to be enhanced in the evening - Not the result of higher muscle fatigability
14
Q
Biochemical Markers of Muscle Fatigue
A
- Many biochemical markers of muscle fatigue (e.g., muscle damage, oxidative stress) are time-of-day dependent.
- Biomarkers of cellular damage + leukocytes have been shown to be higher in the evening compared w/ the morning during:
○ Repeated sprint exercise [15] - Hammouda et al.
○ 30-second Wingate test [16] - Hammouda et al. - Additionally, Hammouda et al. [17] showed that blood lactate + glucose responses to a Yo-Yo intermittent recovery test were higher in the evening than the morning.
- May indicate a greater anaerobic contribution to energy production (i.e., higher mobilisation of glucose metabolism at this time-of-day).
- Also, could be associated w/ greater anaerobic exercise perf in the evening?
15
Q
meta analysis
A
- A meta-analysis conducted by Kentiba et al. [18] revealed that the skeletal muscle injury markers including lactate dehydrogenase (LDH), creatine kinase (CK), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and white blood cells (WBC) possess diurnal variations following exercise.
- The reason for the diurnal variations (i.e. higher at PM) following exercise in these markers has remained unclear ?
16
Q
Circadian Clocks
A
- Central clock: suprachiasmatic nucleus (SCN) of the brain.
○ Light is the major entraining factor for the SCN. - Peripheral clock: skeletal muscle + bone.
○ Regulated indirectly by photic stimulation from the central clock in the SCN using neuro-humoral + temp signals + numerous zeitgebers
17
Q
Clock Genes?
A
- Clock genes are expressed in skeletal muscle + bones of the skeleton + appear to regulate muscular or bone (osseous)- specific biological function.
- Circadian rhythms in skeletal muscle + bone maintain their homeostasis
- Disturbances of circadian rhythms by social or environmental factors, such as shift work, may result in dysfunctions of skeletal muscle + bone.
- We have genes that are going to be normally expressed within certain periods of time + when we disrupt that = is going to have an effect on how the body regulates itself
18
Q
CLOCK + BMAL1 genes
A
- Circadian rhythms generated through a translational-transcriptional feedback-loop mechanism, in which circadian locomotor output cycles kaput (CLOCK) + brain + muscle aryl hydrocarbon receptor nuclear translocator-like 1 (BMAL1) proteins (receptors to do w/ brain + muscle)
- CLOCK:BMAL1 also contributes to the expression of a large number of genes, called clock-controlled genes (CCGs)
- Zhang et al. [20] found that skeletal muscle expresses ~1600 circadian genes + that more than 40% of all mammalian protein-coding genes are expressed rhythmically somewhere in the body
- The role of the clock for expression of genes is important for the daily maintenance of skeletal muscle.
- Rhythmic + CLOCK-driven pathways in human skeletal muscle affect ~8% of muscle genes [21]
19
Q
Health and Clock Genes
A
- People w/ type 2 diabetes + obesity are known to have poor sleep quality [22, 23].
- These conditions may disrupt the core clock machinery [24].
- Ageing is associated w/ a gradual increase in period length of core clock genes, in addition to the dysregulation of other rhythmic biological processes [25].
- Exercise is known to reset clock genes in skeletal muscle + other tissues = timed exercise MAY help to reset the daily clock + improve pathologically deteriorating circadian rhythms
- A functional biological circadian clock is also essential to the normal secretion of basal myokines in vitro such as interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), + monocyte chemoattractant protein-1 (MCP-1) (Perrin et al., 2015)
- Collectively, these findings show that disruptions in the skeletal muscle molecular circadian clock are strongly associated w/ altered muscle structure, function, + metabolic responses that directly affect overall health
20
Q
Importance of Skeletal Muscle Clock
A
- Skeletal muscle (~40% or more of body mass), important for maintenance of whole-body energy, substrate metabolism, + glucose homeostasis.
- Circadian misalignment in humans results in disturbed energy metabolism + insulin resistance in skeletal muscle [26].
- Regulates protein synthesis + protein degradation.
○ Sleep essential for recovery + to build muscle - Displayed circadian oscillation in genes involved in muscle contraction/growth [27, 28].
21
Q
MICE
A
- BMAL1 knockout mice + CLOCK mutant mice show disrupted skeletal muscle myofilament architecture (including decreased expression of the myofibrillar proteins Actin, Myosin, and Titin), fibre-type shifts, decreased mitochondria volume, impaired mitochondrial respiration, + decreased muscle strength at the single-fibre level [29, 30].
^^when don’t have BMAL1 or CLOCK genes
22
Q
BMAL1 activation
A
- Functional muscle clock allows direct BMAL1-dependent activation of genes promoting favourable responses.
- Muscle clock disruption causes loss of BMAL1-dependent activation + REV-ERB-dependent repression of target genes = catabolic conditions = increases = is bad
23
Q
Circadian Rhythm Regulates Protein Synthesis and Protein Degradation
A
- Acute bout of resistance exercise –> express the IGF-1 –> cascade that goes down to mTOR –> have p70S6K –> protein synthesis –> will block any muscle atrophy or protein translation = good thing = muscle is being stimulated + leading to adaptations favourable to an individual
- When we see there is a block of the BMAL1= leads towards factors that impair the ability of the chain of events = therefore it inhibits mTOR –> produces expression of genes that lead towards degradation of protein
24
Q
Circadian Rhythm: Effects of Diet and Exercise
A
- Diet + exercise represent two major interventions that can suppress the atrophy of skeletal muscle, + have regulatory roles in circadian rhythm.
- Along w/ other zeitgebers are natural phenomena that can affect the circadian rhythm.
○ [31] Zhang et al.
25
Q
Circadian Rhythm and Timing of Exercise
A
- Evidence that exercise-induced contraction + its timing may regulate gene expression + protein synthesis related to muscle anabolism + metabolism [32, 33].
- Importance of “circadian phenotype” on optimal aerobic exercise perf [34], but little research on resistance exercise perf
- Phenotype refers to an individual’s observable traits, such as height, eye colour + blood type. A person’s phenotype is determined by both their genomic makeup (genotype) + environmental factors.
26
Q
Summary
A
- Circadian rhythm of core temp is associated w/ anaerobic exercise perf + muscle strength.
- Other factors independent of heat may regulate circadian exercise perf
- Perceived effort during morning versus evening exercise seems to be unaffected - but may differ when considering factors (e.g. chronotype).
- Muscle perf decrement occurs during evening compared to morning exercise - linked to higher perf in evening.
- Greater muscle damage appears following evening exercise.
- Clock genes regulate muscle + bone function.
- Skeletal muscle clock important for contraction + growth.
- Exercise + diet are important factors that can influence the expression of skeletal muscle clock genes
