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First published online October 18, 2006
Journal of Experimental Biology 209, 4379-4388 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02434

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Interactions between the human gastrocnemius muscle and the Achilles tendon during incline, level and decline locomotion

G. A. Lichtwark^1,* and A. M. Wilson^1,2

¹ Structure and Motion Laboratory, Institute of Orthopaedics and Musculoskeletal Sciences, University College London, Royal National Orthopedic Hospital, Brockley Hill, Stanmore, Middlesex, HA7 4LP, UK
² Structure and Motion Laboratory, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire, AL9 7TA, UK

View larger version (52K): [in a new window]   Fig. 1. (A) Picture of the flat ultrasound probe attached to the leg with 3-motion analysis (CODA) markers rigidly attached to the probe head. The ultrasound probe images the leg in the sagittal plane. (B) A stick figure representing the leg used in the measurements. The blue lines represent the leg and foot, the green lines represent the lines joining the three markers attached to the ultrasound probe to measure its position and orientation relative to the leg, and the red line indicates the measured Achilles tendon length (from the calcaneous insertion to insertion on the MG, as determined with the ultrasound images). For an animation, see Animation 1 in supplementary material.

View larger version (48K): [in a new window]   Fig. 2. Average ankle and knee angle and GM MTU length changes (MTU length) with respect to time during walking (A) and running (B) for downhill (-10%; blue), level (0%; green) and uphill (10%; red) conditions. The shaded areas mark the average stance time across each condition and the pooled 95% confidence interval (± 2 s.e.m.) across all grades for both walking and running is shown with respect to the level condition as the area within the dotted lines. The average standard error across each grade condition was equivalent.

View larger version (84K): [in a new window]   Fig. 3. Average GM fascicle length, pennation angle, MTU length change (MTU length) and enveloped GM and tibialis anterior (TA) EMG signals with respect to time during walking (A) and running (B) for downhill (-10%; blue), level (0%; green) and uphill (10%; red) conditions. The shaded areas mark the mean stance time across each condition and the pooled 95% confidence interval (± 2 s.e.m.) across all grades for both walking and running is shown with respect to the level condition as the area within the dotted lines. The mean standard error across each grade condition was equivalent.

View larger version (10K): [in a new window]   Fig. 4. The average relationship between muscle fascicle length and muscle fascicle angle for walking (solid lines) and running (dotted lines) during downhill (-10%; blue), level (0%; green) and uphill (10%; red) conditions.

View larger version (48K): [in a new window]   Fig. 5. The average Achilles tendon (AT) length change measured directly using the projected MTJ measurement and the corresponding estimates of series elastic element (SEE) length change during walking (A) and running (B) for downhill (-10%; blue), level (0%; green) and uphill (10%; red) conditions. The AT slack length is estimated from the average length of AT during walking on the level at the average time of toe-off. The estimated aponeurosis length change (which includes the proximal GM tendon) is calculated as the difference between the AT length change (relative to the slack length) and the SEE length change. The shaded areas mark the average stance time across each condition.

View larger version (12K): [in a new window]   Fig. 6. Average work loops for walking (solid lines) and running (broken lines) during downhill (-10%; blue), level (0%; green) and uphill (10%; red) conditions during the stance phase of the gait cycle. Approximate medial gastronemius fascicle force is calculated using Eqn 3-5.