LO 5.1: To differentiate between muscle strength and muscle power and use the terms appropriately (two correct answers needed)

For Answer i:   Fundamentally, they come to the same thing so which word you use does not matter.

The terms muscle strength and muscle power are not the same.  Strength relates to force output of the muscle while power introduces time and movement elements. Therapists will usually be referring to strength of a muscle.


For Answer ii:   The word ‘power’ should not be used in a clinical therapy setting as it requires specific measurement using equipment that is not routinely available to therapists. Strength can be categorised by the use of clinical scales and so this is the best route.

This is one of the two correct answers! Power needs measurement of both work done i.e. distance moved per unit of time. Therapists will be familiar with the five point gradation of muscle strength (and variations of this scale) and this is the best system for clinical use. See:

For Answer iii:   Neither strength nor power are the best terms to use as therapists are more concerned with endurance i.e. the muscle’s ability to repeat the contraction for a longer period of time before it becomes exhausted.

Therapists are certainly concerned with endurance but should still know the difference between strength and power, as these will impact endurance.

For Answer iv:   Strength = force output and power = (work/time). As power is work done per unit time and work requires movement to take place, it is much more likely that therapists will have their focus on muscle strength.

This is the second correct answer, so ‘Well Done’ if you have selected both correct answers! You are developing a good understanding of these factors.

LO 5.2: To discuss the difference between mechanical and physiological work and the role of each in training control

For Answer i:   Control training focusses on movement at the joint and specifically the ability to change moment signs. This is mechanical work (movement) and any physiological work done is less relevant.

Mechanical work involves movement and this will require energy expenditure. If the movement is strictly limited to just one joint moving, this could be true – but virtually impossible to achieve without stabilisation of all other joints (and no eyelid blinking!).  All muscle activity uses physiological energy and this is especially relevant in maintenance of static postures.


For Answer ii:   Physiological work by muscles is the most important factor in control training, as control of a joint requires energy expenditure.

Both physiological and mechanical work are important. Both will require energy expenditure. Static postures or isometric contraction i.e. no change in muscle length will use principally physiological work but this is only part of control training.


For Answer iii:   Mechanical work is the distance that the force moves, with the movement taking place in the direction of the force i.e. muscle action that results in movement. Physiological work does not require movement so incorporates static muscle action. It is likely that control training will commence by ensuring a posture can be held (principally physiological work) before progressing to include movement (mechanical work and the physiological work of the muscle action).

Correct!  Well done! An understanding of these two concepts is important in movement control training.

For Answer iv:   The difference between mechanical work (force*distance moved) and physiological work where movement is not necessarily involved is not pertinent to control training. It is the muscle strength that is paramount.

Muscle strength is important but any work done by muscles that involves or does not involve movement will use physiological energy.

LO 5.3: To explain the relationship between strength and control

For Answer i:   Muscle strength is the force output that a muscle can generate and control is the ability to modulate the moment acting at a joint, principally through the moment arm length. Control requires strength and strength cannot be gained without control.

Correct!  Well done.  Control and strength are both elements of the same process of promoting movement control.


For Answer ii:   Strength and control are two distinct elements. Strength relates to the force a muscle can generate while control relates to the stability of a joint by muscle action. Strength and control develop and should be trained separately.

Strength and control are distinct elements but they are very closely related. It may be possible to train each independently but this will depend on there being sufficient strength for the control task. Most often, strength and control will emerge together with control being the principal factor.


For Answer iii:   Strength is paramount as without muscle strength, there can be no control at a joint.

It is certainly true that control requires strength but strength cannot be gained without control. Strength without control could be dangerous.

For Answer iv:   Control is paramount as a joint that has strength but no control is likely to lead to injury.

It is certainly true that strength without control could be dangerous but training control at a joint where the relevant muscles have no strength will be almost impossible. Both strength and control are required.

LO 5.4 To determine the optimal posture for promoting control when weakness is present

For Answer i:   The optimal posture cannot be generalised in this way. Each joint will need to be placed in the anatomical position that most easily facilitates movement.

This answer does not really give much information about managing muscle weakness or what the optimal posture might be.


For Answer ii:   The optimal posture will be the default posture that the patient adopts. If it is, for example, full flexion of the joint, then this will be the best start point for promoting control in the presence of weakness. It is where the patient feels most comfortable and is a familiar posture.

This can often be the ‘obvious’ starting point. It is possible that the patient has some strength at this part of the range of motion of the given joint or if working with gravity counterbalanced. But if working in the upright posture, it is unlikely to lead to success as the moment will be too great. Think of lifting the head from full flexion when in the upright posture: the patient will frequently use a burst of activity and the head lifts but overshoots and goes with some force into full extension. This is not controlled activity and is a strategy that cannot be refined. Start from small movements near the neutral position, especially if upright.


For Answer iii:   The optimal posture will depend on the movements available at the joint or joints involved, the chosen posture (e.g. lying, sitting, standing) and the neutral position of the joint in relation to gravity in that given posture. Once the posture is selected, the neutral position should be achieved, passively if necessary and then small range movements introduced in the desired direction, ensuring that the moment arm remains manageable.

Correct!  Well done. The important factor when there is muscle weakness is to keep the moment small, usually by keeping the moment arm small. The muscle(s) is then more likely to be able to achieve the movement goal.


LO 5.5 To explain the role of error in controlled movement

For Answer i:   If a movement has error, then it is not controlled – by definition!

The opposite is true!  If there is no error, the movement is not controlled. Error – and correction of that error, tells the neuromuscular system ‘where it is and what it need to do to achieve the goal’.


For Answer ii:   Error, in this context, is a movement or a posture that is not precisely the desired movement or posture. As it is not exactly what is desired, practice is required to reduce the error.

Error may be the movement or posture that is ‘not quite right’ but practice is not the missing element here. The focus is that error informs the neuromuscular system and corrective action towards the desired posture is made.

For Answer iii:   A controlled movement will, almost certainly, show some error. In this context, error is the difference between the desired state and the existing state. It is this error, which may be very small but which ensures the movement/postural status is constantly monitored by and known to the control system. Corrections can then be instituted as needed towards the movement goal.

Correct!  Well done. Controlled movements almost always show error.


For Answer iv:   All movement, controlled or uncontrolled, will show error as this determines the stability of the movement that contributes to the posture.

It is true that controlled movement will almost always show error, and uncontrolled movements certainly will show error!