RESISTANCE Flashcards
1
Q
Contraction Types - Isometric
A
- activation of muscle when the joints spanned by the muscle are held in fixed positions
- entails some stretching of tendinous connection and stabilise joint complexes during locomotion and maintenance of posture
2
Q
Contraction Types - Concentric
A
- the muscle is activated and shortens, power is generated and work is done
3
Q
Contraction Types - Eccentric
A
- the muscle is activated and lengthens due to an external force which exceeds that generated by the degree of activation
- occurs during daily activities (e.g. walking down stairs) as work is done on the muscle and energy is absorbed, muscle acts as a brake
4
Q
Contraction Types - Stretch-Shortening and Other Pre-Activation Contractions
A
- combination of different types of contraction occur
- ‘stretch shortening cycle’ = eccentric contraction of the muscle immediately prior to a concentric, power generating phase in running
- leg extensor muscles generate power by concentric contractions but also act as a brake or shock absorber on landing, absorbing some of the Ep and Ek generated in the previous push off by the opposite leg
5
Q
Sargeant, 1999 - Human Muscle Fibre Types
A
- muscles meet demands for different mechanical output by variations in the contractile and metabolic properties of fibres
- human fibres divided into 3 main types, Type I, Type IIa, and Type IIb
- more of a continuum than 3 discrete types they currently are
6
Q
Sargeant, 1999 - Fundamental Muscle Properties
A
- maximum velocity of shortening of muscle fibres = Vmax
- continuum of Vmax values between various types, and also within each type of isoform there is a considerable variability
7
Q
Fundamental Muscle Properties - Length-Tensioning Relationship
A
- isometric tension a muscle can generate depends on its length
- tension is due to the interaction actin and myosin myofilaments within each sarcomere
- as muscle lengthens to its limit, there is an increasing level of passive tension due to stretching
- passive stretch tension is subtracted form active tension
8
Q
Sargeant, 1991 - Muscle Length and Active & Passive Tension
A
Amount of actin-myosin overlap is indicated by:
- short length where A-filaments from opposite ends of sarcomere overlap and force is reduced
- optimum length where the greatest active force is generated due to maximum number of cross bridges
- at long length where there is no overlap and no cross bridges are formed
9
Q
Sargeant, 1991 - Force-Velocity and Power-Velocity Relationships
A
- force varies with the velocity of shortening or lengthening
- as velocity of shortening increases, the force generated falls in hyperbolic fashion, eventually reaching zero at max muscle velocity
- during lengthening, force increases above that attained at zero velocity (isometric) before plateauing
- max power is generated at optimum velocity (Vopt), ~30% of Vmax when force is zero
10
Q
Determinants of Maximal Strength and Power
A
- muscle activation
- muscle size and isometric strength
- muscle size and maximal power
- body dimensions and muscle function
- muscle fibre type and power output
11
Q
Muscle Activation
A
- pre-requisite in determining max force is if the muscle is fully activated
- muscle can be tested for MVC by applying electrical stimulation to muscle or nerve
- can achieve almost-maximal VC’s in isometric exercise
12
Q
Muscle Strength is Determined by Sarcomeres in Parallel NOT in Series
A
- cross bridges act as force generators but are arranged in sarcomere units with opposing forces
- no matter how many sarcomeres are arranged in series the net force will be equivalent to only one sarcomere
- if the muscle is arranged with same number of sarcomeres arranged side by side all contribute to force production
13
Q
Muscle Power and Muscle Size
A
- Power = force x velocity
- total distance will be 4x that of sarcomeres in parallel
- muscular power should be normalised by number of sarcomeres in series and in parallel
- reflected in measurements of muscle volume
14
Q
Muscle Function, Body Dimensions and Performance
A
- sometimes useful to express muscle function in terms of body dimensions (J/kg-1 BM)
- important when body mass must be overcome by the exercising muscle
- this method of scaling is often considered simplistic based on the pattern of muscle use, size and intrinsic function of the muscle group
15
Q
Muscle Fibre Type and Power Output
A
- Vmax and F-V relationship of muscle fibres is strongly determined by the MHC expression
- force and power in relation to velocity for a type I and II fibre population that generate some isometric force but whose Vmax varies
16
Q
Sargeant, 1987 - Muscle Fibre Type and Power Output
A
- larger power output in type II fibres is reflected in data comparing untrained subjects (50% type II) vs ultra distance marathon runners (4% type II)
- endurance athletes max power is only half of the UT subjects even though data was normalised for upper leg muscle mass
17
Q
Sargeant, 1987 - Acute and Chronic Plasticity
A
- exercise can modify muscle properties
- when ex continued to fatigue muscle contractile properties may be acutely transformed towards slower characteristics (Vmax is reduced and muscle becomes less powerful)
- muscle fatigue may be greater at fast movement frequencies
- increase in Tm also modify contractile and metabolic properties
- effect of temp is velocity dependant so increases in Tm will also make muscle faster and more powerful at higher velocities
- greater XBC rate and energy turnover reduce economy
18
Q
Effects of Caffeine Ingestion on Power
A
- member of the methylxanthine family, chemical formula = C8H10N4O2
- common in cola drinks (25-50mg Caffeine per serving)
- energy drinks contain much more ( ~80mg)
- present in chocolate and cocoa products
19
Q
Lopes et al., 1983 Caffeine Ingestion and MVC Performance
A
- significant difference between placebo and caffeine at lower frequencies (10,20 and 50 Hz) but not 100Hz
- caffeine consumption significantly affected performance of muscle contractions at slow to moderate speeds but not higher speeds
20
Q
Methodological Considerations of Caffeine Ingestion Studies
A
- dosages
- participant numbers
- exercise protocols (max, sub-max)
- control of environments (temp, humidity, biometric pressure)
- control of subjects (caffeine users, sensitivity/tolerance to caffeine, age, etc)
21
Q
Mechanisms of Action - Excitation-Contraction Coupling
A
- with excessive caffeine intake there is a heightened SR CA2+ release
- effect may be greater in slow twitch vs fast twitch fibres
- muscles contract in the presence of Ca2+
22
Q
Mechanisms of Action - Blocking Adenosine Receptors in the Brain
A
- adenosine binds to A-receptors that cause nerves to release inhibitory signals that lead to drowsiness and sleep
- caffeine blocks A-receptors and promotes continued nerve activity
- caffeine antagonises adenosine (blocks the receptors), reducing adenosine actions so maintains/increases Ach release leading to continued release of brain cell NA and over-rides fatigue
23
Q
Bird et al., 2005 - Strength Training
A
- many studies show a significant increase in performance with resistance training of sufficient training volume
- but most training studies are short duration (<3 month) and use untrained subjects
24
Q
Factors That Interact to Affect Development and Maintenance of Muscle Mass
A
- exercise
- nutrition
- genetics
- endocrine
- nervous system activation
- environment
25
Andersen et al., 2005 - Nutriton and Resistance Training on Muscle Fibre Size and Strength
- protein group showed significant fibre hypertrophy of trained leg muscles (Type I=18.5±5%; Type II 26±5%), no change in CHO group
- Protein group increased SJ by 9±2%
- protein group improved CMJ by 10±2%, CHO group 7±6%
- isometric and isokinetic eccentric and concentric peak torque at slow velocities increaesed 11-20%, no diff between groups
26
Muscle Growth with Resistance Training
- can be used clinically to treat muscle wasting (cancer, AIDS, burns)
- muscle hypertrophy caused by increase in protein synthesis or reduction in protein breakdown
- net protein accretion = protein synthesis - breakdown
- protein synthesis and breakdown can vary 50-100% over a day due to age, diet and activity (Price et al., 1994)
27
Lexell et al., 1988 - Human Resistance Training
- large variability in number of fibres in a muscle
- between 393,000-903,000 fibres in vastus lateralis
- individual's number is fixed, but size can be increased w resistance training
28
Muscle Protein Synthesis Post-Ex
- remains elevated for more than 48h post-ex in untrained (Rennie and Tipton, 2000)
- protein breakdown also increases (Philips et al., 1997)
- net protein breakdown may occur unless protein is consumed (Tipton et al., 1999)
- mixed meal will increase appearance of AA (increased protein gain) and glucose (insulin decrease protein loss) (Rennie and Tipton, 2000)
29
Muscle Growth and Resistance Training
- max rate of protein synthesis by feeding alone requires 10g EAA's i.e. ~20g total AAs or protein
- need to eat protein and exercise to increase muscle hypertrophy
- Philips, 2004 - upper safe limit of protein intake 1.33g.kg-1BM.d-1
30
Factors Leading to Muscle Hypertrophy
- first messengers binding to receptors causing propagation of cellular signals that activate a network of signal transduction pathways
- cell nucleus TFs change expression of major muscle growth regulators IGF-1/MGF and myostatin or rRNA
- IGF-1/MGF and insulin activate the PI3K-PKB/AKT-mTor pathway, enhances protein synthesis via increased translational initiation and the synthesis of ribosomal proteins for ribosome biogenesis
