Biological Basis of Increasing Muscular Power Flashcards
What is a Power?
- Fast twitch vs slow twitch fibres
Where power is the product of Force and Velocity (p = f*v)
Could be measured by
- Velocity of bar movement
- Rate of force development (isometric, isokinetic testing modes)
- Explosive performance (speed, acceleration, vertical jump height)
Fast 2A has a greater velocity and power producing capacity at any given force while Slow fibre have the lowest
Why do we care?
- Maximal force output of a muscle typically takes >300ms to develop
- Many sporting applications (striking a ball i.e. golf; striking a person; kicking a ball; throwing; sprinting; Olympic lifting) require performance to occur in time periods <200ms
- Therefore the rate at which we can develop force (rate of force development) is probably the most important factor in terms of athletic performance. Also seems to be where muscle activation loss during exercise has it’s most profound effect
- Related to injurie mechanisms, discriminate starter and non starter status in some sports
- Important for falls prevention
What explains power?
HINT: 2 points
- Intrinsic muscle properties
- Neural improvements
Intrinsic muscle properties - muscle fibre type
- Association between the…
- Association between the rate of rise in the resting twitch (i.e. the force we get out of you from stimulation along) and voluntary rate of force development
- As you get closer to 250 to 350ms your ability to produce MVC and RFD is going to get closer
- (Study) Those with greater percentage of fast twitch fibres respond with a greater rate of force development
Neural Components
- Power training
- STUDY: Changes in single motor unit behaviour contribution to the increase in contraction speed after dynamic training in humans ( 12 weeks of training)
- Neural drive (V & H wave)
- Motor unit recruitment
- Rate coding / discharge rate
- Motor unit synchronization
- Recurrent Inhibition
Power training encourages us to recruit more motor units as quickly as possible
Motor unit synchronisation is almost perfectly correlated to discharge rate
Study:
- After twelve weeks of training, there was minimal changes between twitch characteristics suggesting that any changes that we see of we do see changes would be coming from EMG or the ability of the nervous system to stimulate the muscle
- Rate of force development was higher after training
- Post training, there was a drastic increase in the quality and the amount of the motor discharge rate form the nervous system
Neural components
- MU recruitment & discharge rate
- normal resistance training vs power training
- V wave
EDIT FIRST POINT
- Motor unit recruitment speed probably more improbable than discharge rate for early RFD
- Discharge rate probably explains increases in force output
With normal resistance training , there is an increase in MU discharge but with power based you get a greater amount of motor unit recruitment and discharge
V wave: supraspinal drive. As the V wave increases relative to the M wave we see a strong correlation between the amount of rate of torque development an individual can produce.
What explains how we generate power?
- Morphology -
- Most of the rate of force development can be broken down into two section. Your ability to produce force rapidly is up to around 75ms seems to be driven by how well your nervous system can recruit as many motor units as quickly as possible. Your ability to produce rate of force development in later phase from around 75ms onward seems to be driven by the intrinsic muscle properties (e.g. the number of fast twitch muscle fibre you have).
- Neural get the system going and how quickly it can turn over once you get it fired up depends in intrinsic muscle properties.
Morphology - how we generate power?
- Men vs women; similar proportion of the different fiber types, all fiber types large in men, but disproportionately so for the type II fiber (men have higher proportion of muscle area from the type II isoform, women higher area from type I) Same ‘number’, they’re just bigger for men
- Supraspinal output
- Ability to rapidly recruit type II motor units (and maintain a high firing rate)
- SO if we can increase any of these with a training program, we are likely to increase POWER
Historical findings for muscular power output
- Fmax
- Kaneko (1974) studied the time course of changes in elbow flexor force‐velocity and mechanical power with respect to different training intensities (0, 30, 60, 100% MaxForce) for a period of 20 weeks
- Kaneko observed that training with 0% Fmax was most effective for increasing unloaded contraction velocity
- Training at 100% Fmax most effective for increasing muscle strength
- Training 30% Fmax most effective for increasing peak muscular power in isolated muscle actions
- Although supported (Caiozzo, 1981; Coyle, 1981; Moffroid and Whipple, 1970) no other measures had been performed thus far to explain why muscular power was increased
Historical findings for muscular power output - not so simple
- power adaptation in novices during strength training
- In reality – a range of peak power (Pmax) exist across a range of exercises hence recommended optimal power can range from 0- 80% of 1rm.
- E.g. Jump squat vs Power clean.
- See Cronin & Sleivert 2005 ; Challenges in understanding the influence of maximal power training on improving athletic performance”
- 3 groups (strength, power & control)
- Novices who do strength training get adaptations for strength and for power. Suggest that you will get more power when you get stronger through strength training.
- Stronger group had more power adaptations earlier than the weaker group
Power adaptations from RT programs - Trained
STUDY: Changes in isometric force- and relaxation-time electromyographic and muscle fibre characteristics of human skeletal muscle during strength training and detraining
HINT: 24 week training protocol. Included progressive overload
-24 week training protocol. Included progressive overload
- Small adaptation from EMG activity from trained group
- Hypertrophic factors and changes in force-time characteristics occurred over the first 12-weeks of training
- Suggested that the specificity of training, or lack thereof, from 12-24 weeks influenced the lack of ability to cause adaptation in early force development characteristics - didn’t include power training
- Seeing an increase in the rate of force development around 150 to 200ms. Looking at early rate of force development there isn’t much difference between the trained and untrained groups. It was suggested that the reason for this is because the program did not include power-based training
Power adaptation from RT programs- Trained
STUDY: Effect of explosive type strength training on isometric force- and relaxation-time, electromyography and muscle fibre characteristics of leg extensor muscle
HINT: 24 weeks training protocol. Included power based training
- 24 weeks training protocol. Included power base training
- Greater EMG activity with power based training
- The inclusion of power-based exercises to resistance trained individuals was enough to cause an increase in the early phases when we start to see adaptation (in average force)
Power adaptations from long term RT programs
HINT: Strength training in two years:…
Most findings to date (and even now in 2020) represent the changes and responses of untrained individuals to resistance exercise, or a short duration training programs in well training individuals
It is expected that responses in elite athlete will be of a lower magnitude, but there is limited evidence examining changes over time
- Strength training in two years: minimal changes in maximal isometric force and EMG
- Room for adaptation for trained individuals is diminished
Power adaptation from RT programs - Novice
STUDY: Increases rate of force development and neural drive of human skeletal muscle following resistance training
HINT: four weeks of resistance training in novices…
Four weeks of resistance training in novices: Small improvements in RFD in earlier phases from just doing progressive overload resistance training. Peak RFD also increases at all time points
- Also saw improvements in mean amplitude (of EMG)
- Even though they didn’t do any specific power based training, they were able to infer changes to ballistic of contractile RFD
Power adaptations from RT programs - Caveats - Novices
STUDY: Early and late rate of force development: differential adaptive responses to resistance training
HINT: Contractile RFD in earlier and later phases of …
- Contractile RFD in earlier and later phases of rising muscle force responded differently in response to resistance training
- The neural adaptations related to strength gains in novices are also associated with influencing the ability to produce force rapidly, and this neural adaptation provides a powerful contrast to the negative contribution a phenotype shift (type II x to type II a) may have on explosive force production following resistance training
We can still get improvements in the early phases of RFD in a progressive resistance training if we tell the individuals to contract as quickly as possible
The isometric training group appears to have a larger difference than the concentric group. Both groups were told to contract as quickly as possible.
No matter what movement you’re doing, as long as you are thinking that you are trying to move the barbell as fast as you can, we seem to still be able to get good neural adaptations to those early phase contractile windows.
Power adaptations from RT programs
- Novice
- Trained
Novices
- Increases in power can be seen via basic RT programs. May question whether power based training should be the focus of a RT program for novices.
- Changes in neural adaptation seem strong enough to overcome possible detriments from Type 2x conversion to 2a.
- Early phase RFD may remain unchanged if lifting “intent” is not maximal. e.g. (lift as fast as you can regardless of the actual velocity of movement)
Trained Populations
- RT programs alone probably not specific enough to cause wanted power adaptations to trained populations.
- Addition of ballistic style and power based exercises to RT programs does seem to cause wanted power adaptations.
- Overall, not a lot of evidence for chronically / elite trained population.
