Leg muscle activity patterns during walking in healthy young and old adults

When walking at similar speeds, profound differences in the walking pattern and
its underlying neuromechanical control have been observed between healthy young
and old adults. For example, old adults take shorter steps, have more variable
steps, lean more forward with their trunk, have a lower ankle range of motion,
generate less ankle positive work and greater hip positive work (i.e.
redistribution of concentric muscle function), and stiffen their legs more
through greater shank and thigh co-contraction. Recently, we observed no
age-related differences in the distribution of negative leg joint work or
eccentric muscle function during walking. This may be due to the relative
maintenance of maximal voluntary eccentric compared to concentric muscle
strength in old age. That is because muscle weakness with aging is one likely
factor contributing to the reduction in plantarflexor positive work during
walking in old age. As both neural and skeletal muscle properties make up force
production control and the neural control differs between eccentric and
concentric muscle contractions, it seems relevant to determine whether
age-related difference in muscle activation patterns during walking are also
muscle contraction-specific.

Previous studies that examined muscle activation patterns during specific
phases of walking in young and old adults can be used to some extent to
formulate hypotheses for muscle contraction-specific activation patterns due to
age. That is because a selected phase does not necessarily capture only one
muscle contraction type or only a part of it. Nevertheless, one study observed
greater soleus, vastus lateralis, and rectus femoris muscle activity in the old
during the loading phase (~eccentric function) of level walking, and lower
soleus activity during push-off (~concentric function). Another study, however,
observed comparable muscle activities of leg extensor muscles during the first
half of stance (~eccentric), even when walking downhill. Their results also
indicated a tendency for greater soleus activity and greater gluteus maximus
activity with increasing uphill walking in the old during the second half of
stance. Since downhill and uphill walking compared to level walking
respectively accentuates eccentric and concentric muscle function, these
previous findings may suggest that the neuromuscular control of concentric
muscle function during level and uphill walking but not eccentric muscle
function during level and downhill walking is different between young and old
adults.

Main objective: To determine the effects of age and surface inclination on
muscle activation during positive and negative joint work.
Secondary objective: To determine if walking on an inclined surface magnifies
age-differences in muscle activation compared with level walking.

This observational cross-sectional study consists of one session in which a
subject is asked to perform functional activities of daily living (i.e. static
balance, sit-to-stand, 3-meter walking) and to walk several times on level and
inclined surfaces over short distances (i.e. ~10 meters).

The subjects will visit the Center for Human Movement Sciences once. The
subjects are asked to perform activities of daily living. Risks are minimal and
comparable to daily life. The subjects can rest in between measurements if
necessary.