Theme 1

Question 1

What is the equation for central activation ratio (CAR)?

Answer 1

MVC / (MVC + SI)

Question 2

What is the equation for Interpolated Twitch Technique (ITT)?

Answer 2

1 - (SI/RT) x 100

Question 3

What is the definition of CAR?

Answer 3

Central Activation Ratio (CAR) is the ratio of the force produced during a maximal voluntary contraction (MVC) to the force produced when an additional electrical stimulus is superimposed on that contraction.

Question 4

What is the definition of ITT?

Answer 4

Measures how fully a muscle is voluntarily activated by comparing stimulation-evoked force during a maximal contraction to that evoked at rest.

Question 5

How are CAR and ITT different?

Answer 5

Although they give similar information, they differ in what they measure to get the result.
CAR uses MVC and SI, whereas ITT compares SI size to resting twitch size.

Question 6

Muscle activation capacity definition

Answer 6

The extent to which a muscle can be voluntarily activated by the nervous system during a maximal effort.

Question 7

Neuromechanical/Electromechanical delay (EMD) definition

Answer 7

The time lag between the onset of muscle electrical activity and the start of measurable force.

Question 8

Muscle activity definition

Answer 8

The electrical signals generated by a muscle during activation, measured using EMG. It provides information relating to the timing, frequency and magnitude of muscle activation.

Question 9

Rate of force/torque development (RFD/RTD)

Answer 9

The speed at which force or torque increases during the early phase of muscle contraction, typically within the first 50-200ms.

Question 10

What are the three practical issues when conducting EMG assessment?

Answer 10

Noise/Interference
External factors (electrode application and setup)
Intrinsic factors (physiological and participant-related variables).

Question 11

What is validity in relation to EMG?

Answer 11

Refers to whether EMG accurately measures what it intends to (true muscle electrical activity and activation patterns).

Question 12

What is reliability in relation to EMG?

Answer 12

Refers to the consistency of EMG measurements when repeated under similar conditions.

Question 13

What noise/interference issues affect validity?

Answer 13

Electronic noise - arises from surrounding equipment which emits electromagnetic interference and can mask the muscle signals. Complete masking can occur with low-intensity contractions as EMG signals are small.
Motion artefacts - movement of the electrodes on the skin or cables in wired systems generate low-frequency noise that distorts the true EMG signal.

Question 14

How to mitigate noise issues relating to validity.

Answer 14

Conduct testing in an environment with as little technology interference as possible, or an electromagnetically shielded environment.
Secure cables to minimise movement.
Use signal processing techniques to reduce noise effects.

Question 15

What are the external/extrinsic issues relating to EMG validity?

Answer 15

Electrode placement - electrodes must be positioned over the muscle belly, aligned parallel to muscle fibres and places with consistent inter-electrode distances. Misplacement leads to cross-talk from adjacent muscles or weak signals.
Skin preparation - hair removal and cleaning with alcohol reduces skin impedance (resistance to electrical current) and improves signal quality.
Electrode type and quality - improves signal detection. Surface electrodes capture a broad area, increasing noise risk, intramuscular electrodes provide specificity but are invasive.

Question 16

What are the internal issues relating to EMG validity?

Answer 16

Variability in skin temperature and hydration affects impedance. Dry, cold skin increases resistance, sweat causes artefacts.
Physiological variability - muscle physiology - the number of active motor units, their firing rates and the muscle’s fibre type influence amplitude. Subcutaneous fat also attenuate signals, especially in sEMG.

Question 17

How are external issues in relation to validity mitigated?

Answer 17

Use standardised electrode placement protocols - SENIAM guidelines. Ensure consistent orientation and spacing.
Properly prepare the skin.
Use good quality electrodes.

Question 18

How to mitigate internal issues relating to validity?

Answer 18

Normalise results e.g. express as a percentage of maximum voluntary contraction to reduce inter-subject variability

Question 19

What are the noise issues affecting EMG reliability?

Answer 19

Equipment and environment - different levels of noise between different environment. Different cable movements, or electrode conditions.

Question 20

How to mitigate noise issues relating to EMG reliability?

Answer 20

Secure cables, maintain a technology free environment where possible, use adhesive electrodes with good contact or pre-gelled electrodes for consistent conductivity.

Question 21

What are the external issues relating to EMG reliability?

Answer 21

Electrode placement consistency - small variations in electrode location, orientation or inter-electrode distance between sessions cause variability in signal amplitude and frequency.

Question 22

How to mitigate external issues with EMG reliability?

Answer 22

Use standardised electrode placement protocols.

Question 23

What are the internal issues with EMG reliability?

Answer 23

Skin condition - changes in hydration, temperature, or skin impedance between sessions influence signal quality.
Participant factors like motivation, effort and movement strategy introduce variability that reduces reliability.

Question 24

How to mitigate internal issues with EMG reliability?

Answer 24

Standardise room temperature, time of day water intake etc.
Instruct participants clearly to maintain consistent effort and technique.

Question 25

What are the effects of training status on muscle activation capacity?

Answer 25

Del Balso and Cafarelli (2007) 4 weeks of resistance training using 6 sets of 10 MVCs. Voluntary activation assessed by ITT increased by 2.8%, p < 0.001 over 4 weeks. Significant effects were seen within three days increasing from 97.2 +/- 1.3 to 99.1 =/- 0.7%, p < 0.002.

Question 26

What are the reasons for increased muscle activation capacity with training?

Answer 26

Increased neural drive - can recruit more motor units. Decreased inhibitory mechanisms - golgi tendon organ sensitivity decreases, less inhibition = more motor unit activation. More effective motor output to the muscles from the spinal cord to the muscles - increased excitability of motor neurons, improved synaptic efficacy, and enhanced motor unit firing rates.

Question 27

How does training status affect muscle activity?

Answer 27

Del Balso and Cafarelli (2007) 4 weeks of resistance training using 6 sets of 10 MVCs. The surface EMG increased by 60.7 +/- 30.8% from day 1 to 13 p < 0.001. And was significant by day 7 (p < 0.001). Juha and Keijo (2009) Strength athletes showed higher EMG activity than non-athletes during forced repetitions who also had lower baseline activation.

Question 28

What are the reasons for increased muscle activity with training status?

Answer 28

Increased motor unit recruitment, firing frequency and synchronisation = higher amplitude. Early gains are primarily neural, not muscular - not increased muscle mass or changes in fibre type. Reduced co-contraction of antagonist muscles - higher amplitude due to more focused activation of the target muscle - more efficient agonist EMG signals and higher net torque.

Question 29

What is the effect of training status on electromechanical delay? Impact of change on performance?

Answer 29

Smith et al., 2021 EMD decreased after 4 weeks of resistance training. Effects split by baseline to 2 weeks, 2 weeks to 4 weeks. Both the electrochemical and mechanical components decreased significantly. Significant effects were seen first in the electrochemical component and then mechanical component. Baseline to week 4 p < 0.001 for all three. Chemical, mechanical and overall. Enhances responsiveness in dynamic tasks like change of direction, can quickly produce a force that propels the athlete in the desired direction, or can quickly decelerate/accelerate when needed etc.

Question 30

What are the reasons for reduced EMD with training?

Answer 30

Electrochemical Faster calcium release and reuptake. Shortens the time needed to generate force at the fibre level. Enhanced motor unit firing rate and synchronisation - more immediate and coordinated force output - larger force produced quicker. More recruitment of fast-twitch muscle fibres responsible for powerful, rapid contractions. Mechanical Increased tendon and muscle stiffness - transmits force more rapidly because less time is spent taking up the slack - stretching tissues to make them taut. Reduced initial tendon slack - elastic components of the muscle tendon unit become engaged sooner during contraction. This reduces the time lag between muscle fibre contraction and force production.

Question 31

What effect does training status have on RFD?

Answer 31

Del Balso and Cafarelli Maximal rate of torque development increased significantly. It had increased significantly by day 5 p < 0.005. After 4 weeks there was a 33.1 +/- 26.2% increase (p < 0.006). Rate of twitch torque relaxation also significantly increased which supports RFD by improving the timing of repeated contractions and reducing interference from prior contractions. There was also a significant increase in the activation rate of the muscle. 48.7 +/- 24.3% increase p < 0.001. This indirectly affects RFD as force can be generated quicker as motor units are recruited faster. Aagaard et al., 2002 14wks of resistance training with a strength and power rep range of 4-6, EMG signals showed a 22-143% increase in amplitude within the first 100ms. This is particularly important in explosive actions like jumping or sprinting. It is also particularly responsive to neural adaptations.

Question 32

What are the reasons for increased RFD with training?

Answer 32

Increased neural drive - motor unit recruitment and firing rate - faster build up of force. Increased synchronisation - enhances initial force. These primarily affect early phase RFD - within the first 100ms. Increased recruitment of fast twitch fibres.

Question 33

How is RFD affected by other variables?

Answer 33

The changes in muscle activity, electromechanical delay, and activation capacity collectively enhance rate of force development. Increased EMG amplitude and faster motor unit recruitment allow force to build more rapidly, while reduced EMD shortens the delay between activation and force output. Greater voluntary activation enables quicker recruitment of high-threshold motor units, particularly type II fibres. Together, these adaptations allow for a steeper and earlier rise in force, improving RFD with training.