1. Recognising features due to
neuromuscular impairments –
weakness
Richard Baker
Professor of Clinical Gait Analysis
1

2. What is muscle “weakness”?
2

3. Strength
the ability to generate a normal voluntary
force in a muscle or normal voluntary torque
(moment) about a joint.
This is different to engineering definitions of strength which focus on
how difficult it is to break something
3
NIH Task force on Childhood Motor Disorders
Sanger, T. D., Chen, D., Delgado, M. R., Gaebler-Spira, D., Hallett, M., & Mink, J. W. (2006).
Definition and classification of negative motor signs in childhood.
Pediatrics, 118(5), 2159-2167

4. Weakness
4
muscle fibre length
Pennation angle (q)
muscle volume
Physiological cross sectional area = muscle volume
Fibre length x cos(q)
Strength is determined primarily by
physiological cross sectional area

5. Muscle belly length
5
Shortland AP, Fry NR, McNee AE, Gough M. (2009) Muscle structure and function.
In Gage JR, Schwartz MH, Koop SE, Novacheck TF. The identification and treatment of gait problems in cerebral palsy. London: Mac Keith Press
half fibre width/ half muscle belly length

6. Muscle belly volume
6
Shortland AP, Fry NR, McNee AE, Gough M. (2009) Muscle structure and function.
In Gage JR, Schwartz MH, Koop SE, Novacheck TF. The identification and treatment of gait problems in cerebral palsy. London: Mac Keith Press
half fibre width/ half muscle belly length

7. Muscle belly volume
7
Barber, L., Hastings-Ison, T., Baker, R., Barrett, R., & Lichtwark, G. (2011). Medial gastrocnemius
muscle volume and fascicle length in children aged 2 to 5 years with cerebral palsy. Dev Med Child Neurol, 53(6), 543-548.
half fibre width/ half muscle belly length
2-5 years olds.
Mean Dorsiflexion with
knee extended = 8°

8. Activation
8
Stackhouse, S. K., Binder-Macleod, S. A., & Lee, S. C. (2005). Voluntary muscle activation,
contractile properties, and fatigability in children with and without cerebral palsy. Muscle Nerve, 31(5), 594-601.
Weakness is both neurological and muscular

9. Muscle weakness
9
Wiley, M. E., & Damiano, D. L. (1998). Lower-extremity strength profiles in spastic cerebral palsy.
Developmental Medicine and Child Neurology, 40(2), 100-107.

10. Measuring muscle strength
10

11. Manual muscle testing
• MRC
• Oxford
• Kendall
11
Medical Research Council (1943) Aids to the examination of the peripheral nervous system
Kendall, HO, & Kendall, FP. (1949). Muscles Testing and Function. Baltimore: Williams and Wilkins.

12. Manual muscle testing
12
O'Brien, M. D. (2010). Aids to the examination of the peripheral nervous system: W.B. Saunders.

13. Manual Muscle Testing
• Essentially subjective
• “Through range
• Gravity on distal segment
13

14. Other techniques
• Hand held dynamometry
• Biodex/Kincom
14
Taylor, N. F., Dodd, K. J., & Graham, H. K. (2004). Test-retest reliability of hand-held dynamometric
strength testing in young people with cerebral palsy. Arch Phys Med Rehabil, 85(1), 77-80.

15. Recognising weakness from
the graphs
15

16. Kinetics
16
Fosang, A., & Baker, R. (2006). A method for comparing manual muscle strength measurements with joint moments during walking.
Gait Posture, 24(4), 406-411.

17. Kinetics
17
Dallmeijer, A. J., Baker, R., Dodd, K. J., & Taylor, N. F. (2011). Association between
isometric muscle strength and gait joint kinetics in adolescents and young adults with cerebral palsy. Gait Posture, 33(3), 326-332.