Reading research: Biomechanical walking pattern changes in the fit and healthy elderly

So recently, I’ve looked at a couple of studies relating to older people.

Firstly, I reviewed an article about the differences between hormone responses to resistance exercise in younger and older men.  And then, last week, I looked at a review article that covered a range of studies on how resistance exercise helps older people reduce the effects of wha they perceive as ageing (but may actually be primarily inactivity).

And while there are dozens of studies around that talk about how older people can help reduce the effects of inactivity, I have not seen much discussion of how actual their biomechanical walking patterns change.

***

So what’s the study today?

The study today takes us on a journey to look at how the biomechanical walking pattern of people changes as they get older.  See if you can spot why it happens…

The study is rather optimistically called Biomechanical walking pattern changes in the fit and healthy elderly, by Winter, Patia, Frank and Walt, in Physical Therapy, 1990.  I say optimistically because I think they may be making some incorrect assumptions about what “fit” means in the context of older people.

***

So what is the point of the study?

Well, the reason for the study, of course, is to enable the researchers to understand more about why old people seem to fall down a lot as they get older.

In general, the investigation into old people and falls is rewarding quest undertaken by many noble researchers.  In the various studies I have read, some of them seem to really understand the fact that the people they are testing are simply inactive and weak.  Others, unfortunately, do not comprehend this idea at all and from those parties we get somewhat involved hand-wringing about the possibility of balance being harshly affected by age and other strange notions.

So what’s the connection between falls and walking?

***

Walking is falling over

The important thing to note about walking is that the initiation of walking itself from a standing position is fundamentally a destabilising motion.  The body’s centre of gravity is made to fall forward and only the moving forward of a foot stops the body from falling onto the ground.

When a number of steps have been taken with a normal gait, and we are in motion, the body is frequently in an unstable position, in that one foot is in the air.  The researchers note that this takes place 80% of the time.

The only time that there are two feet on the ground, one foot is pushing off the ground with considerable force while the other foot is accepting the full weight of the body.  In the case where the rear foot is pushing off and the front foot is bearing the weight, neither foot is flat on the ground, as the force in the rear foot is on the ball of the foot and the front foot takes much of the weight on the heel.

So, during normal walking, the body is in an inherent state of instability.

***

So what is hard about walking?

Our researchers describe two basic challenges to balance when walking:

• The upper body - since the upper body comprises about two-thirds of the average person’s body mass, and it’s centre of mass is about two-thirds of body-height above the ground, this unstable mass or “odd object” needs to be controlled.
• The foot - the foot presents an interesting challenge during the swing phase of gait, firstly as it needs to pass the other foot safely without hitting it (or the ground).  How many people do you know who have tripped over their own feet?  Quite a few.  And secondly, there needs to be a gentle foot landing so avoid damage to the foot or shock to the body that throws it off balance.

***

So how does the body prevent the upper body from falling forwards?

Well, it’s not the muscles around the ankle

While research has shown that the muscles controlling movement at the ankle are involved to control the upright posture when standing, they do not perform a similar role when walking, as the strength requirement would be too great.  It would look like a free-standing glute-ham raise or something out of the Matrix.

Dodging bullets or forgetting how to walk properly?

***

So rather than require the ankle to do any real work when the upper body tips forward and the hip angle starts to close, the ankle muscles produce a small dorsiflexor moment to lower the foot into the ground, followed by a small plantar-flexor movement to control the forward leg.

***

It must be the hip and knee muscles, then

Indeed, that is correct.  But remember what we said just now about doing a standing glute-ham raise?  It is (or should be) the hip extensor muscles that intervene to prevent the upper body from falling forwards.

The hip extensor muscles are the gluteus maximus and the hamstrings.

***

So how does the body prevent the foot from catching on things?

With difficulty, to be honest.  Our intrepid researchers note that in other studies, the swing phase of gait has been shown to be executed with considerable precision, with average toe clearances of just 1 cm, and this clearance occurs while the horizontal velocity of the foot is at its highest.

So any degeneration in the fine motor control of the foot would naturally result in quite serious problems, including stumbling during the swing of the foot.

***

So what did the researchers do?

To help them measure the exact walking pattern of older people to see if there was a comon theme, they took 15 elderly subjects and stuck reflective markers on the following joint centers and segments: toe, fifth metatarsal, heel, lateral malleolus (ankle), head of the fibula, lateral epicondyle of the femur (knee), and greater trochanter (hip).

Then they got each subject to walk at their natural cadence on a level walkway a minimum of 10 times.  A video camera recorded the marker trajectories over the stride period.  Also, each subject walked over a force platform.

They used a control group of younger people so that they had a standard to measure against.

***

What did they find?

 The researchers found that:

• Cadence (number of steps per minute) - the natural cadence of these fit and healthy elderly adults was no different than that of the young adults.  This differed from previous studies, in that cadence was found to be lower in older people.  The researchers put this down to the fact that they had screened to find only “healthy” older people.
• Stride length – the stride length of the older people was significantly shorter, independent of whether it was stated in absolute terms or as a fraction of body height.
• Stance time (time spent with both feet on the ground) - associated with the shorter stride length was an increase in the stance time.  This was not large in absolute terms but it was statistically significant.
• Toe clearance - interestingly, the toe clearance for the elderly subjects was not statistically different from that of the younger adults.
• Index of upper body balance – the researchers measured the covariance of the moments about the knee and the hip, which is an index of how able the subjects are to control the upper body.  Ideally, from a mechanical point of view, it should be fairly close to 100%.  They found that the young subjects scored an average of 67% but the elderly subjects only scored 57%.  The researchers suggested that this means that the elderly are less able to make the shifts in the moment patterns on a stride-to-stride basis to control the balance of the upper body in the sagittal plane and at the same time maintain the extensor support moment.  I would suggest it means that the older people had a weaker posterior chain.
• Push off force – the push-off generation of force from the rear foot by the elderly subjects was considerably less than that of the younger subjects, which explains why their cadence was similar but their stride length was much shorter.  The researchers suggest two possible reasons for this: firstly, that it might have been done deliberately to reduce the potential for instability; and secondly, that it might be caused by a decrease in leg strength.

***

So what are the conclusions?

The researchers conclude that the important discoveries here were:

• The natural walking speed of the elderly subjects was significantly reduced but not because of cadence, but rather because of a reduction in stride length.
• Toe clearance in the elderly subjects was not significantly different from that of the younger adults.
• The index of upper body balance was reduced slightly in the elderly subjects.
• The push-off force was lower in the elderly subjects.

The researchers don’t try to conlude anything further from their work so let me paint a picture…

• Toe clearance – the fact that there is no change to toe clearance supports my view that when elderly people trip over, it is for the same reason that a younger person falls over.  It happens from time to time because the clearance is small and the foot is travelling quickly and people are not naturally very co-ordinated any more because we lead sedentary and unathletic lives (even our non-sedentary pursuits tend to be unathletic).  So why do old people fall more often and hurt themselves?  Because they are not strong and athletic enough to recover once they do lose their balance.
• Upper body balance – this is reduced because the hip extensors (gluteus maximus and hamstrings) weaken faster than the hip flexors and knee muscles (old man butt syndrome).
• Fit and healthy subjects – I think the biggest error that these researchers made was to assume that “active” by today’s standards was sufficient to provide an indication of a healthy elderly person.  I don’t agree with that.  I think that the exercise requirements necessry to produce a healthy elderly person are much more stringent and involve resistance training, not just the treadmill.  I believe that these subjects were weak because of a lack of muscle mass and proper exercise and therefore demonstrated poor walking patterns because of this, not because they were old.