Many falls occur in older persons during stair descent and in this research carried out by Dr Sally Lark, who was a PhD student working under the supervision of Professor Anthony J Sargeant and Professor David A Jones, it was demonstrated how dynamic stiffness of ankle and knee joints leads to the elderly adopting different strategies for descending stairs
OBJECTIVE: To compare the joint torque pattern and dynamic joint stiffness at the knee and ankle in elderly and young men during stepping down.
BACKGROUND: Adequate joint stiffness is critical during the single support phase to control forward and downward body momentum.
DESIGN: Six active elderly men (mean 67.7) and six young men (mean 23.6) of similar body mass and height, were filmed stepping down from one force platform to another. Repeated trials were undertaken at three different step heights (200, 250, and 300 mm).
METHOD: Joint torques were determined for the ankle and knee of the support limb throughout the single support phase. The gradient of the joint torque-angle graph was calculated to define dynamic joint stiffness of the ankle and knee in two phases; (I) from initiation of movement until heel-off of the supporting limb, and (II) from heel-off of the supporting limb to contra-limb touch down.
RESULTS: Maximum ankle torque values were lower in the elderly and occurred at a larger dorsiflexion angle (P<0.05). Knee torque patterns were similar in both groups. Phase I ankle stiffness was significantly less in the elderly (4.0-5.2 Nm/ degrees ) at all step heights compared to the young (7.6 – 8.7 Nm/ degrees ). In both groups ankle stiffness in Phase II increased with step height, while knee joint stiffness decreased.
CONCLUSIONS: The different torque pattern and lower dynamic ankle stiffness in the elderly, particularly for Phase I, suggested an altered control strategy. These findings highlight the importance of dynamic ankle joint stiffness in stepping down.
RELEVANCE: Understanding how the elderly step down may be important in developing strategies to prevent falls
This 1975 research published by Professor Anthony J Sargeant and Professor CTM Davies could find no evidence for a reduction in human aerobic performance due to circadian rhythm. It seems more likely that any reduction in performance as a consequence of movement across time-zones is simply due to lack of sleep or general dietary and other lifestyle disruption.
The responses of six healthy male subjects to submaximal and maximal exercise on a stationary bicycle ergometer have been investigated over a 24-hour period. Measurements were made on each subject at approximately three-hourly intervals and they included minute ventilation at a carbon dioxide output of 1-5 1 min-minus 1 (VE 1-5), tidal volume at a fixed VE of 30 1 min-minus 1 (VT 30), oxygen intake (VO2) at a work load of 150 W (VO2 150), tympanic temperature (Tty) and cardiac frequency at a VO2 of 1-5 1 min-minus 1 (fH 1-5). The experiments were conducted in three parts: on the first occasion two subjects were measured during exercise; on the second occasion a further four subjects were observed in a similar way but starting from a baseline of zero load, and the measurements also included an estimate of cardiac output (Q) using a rebreathing technique.
Finally the maximum aerobic power output (VO2max) was measured in three of the subjects in early morning and late evening. Diet and habitual physical activity were held constant between the exercise test on all three occasions. The results show that in the first two subjects fH 1-5 and Tty had a rhythmic pattern of variation with time of day whereas VE 1-5, VT30, and VO2 150 remained fairly constant. The variation in fH 1-5 was associated with Tty; the two variables reached a minimum at similar to 0500 hr and a maximum at similar 1200 hr. These results were confirmed on the remaining subjects but the changes in fH 1-5 and Tty were shown to be more variable and reduced in magnitude. Further, if the changes were calculated from a baseline of zero load, it was shown that the absolute changes observed in fH 1-5 and Tty were not due to the exercise per se but to changes in the basal level from which each subject operated. In addition it was shown that VO2 max and Q remained constant and were independent of the time of day. It is concluded that provided the exercise test conditions are rigidly standardized and subjects exercise from a controlled baseline there is no evidence for circadian variation in the change of responses to work at submaximal or maximal effort
This research was carried out at The Brompton Hospital in London in the paediatric department of Professor Simon Godfrey. It showed that the the aerobic performance measured as maximum oxygen uptake was surprisingly the same for obese and non-obese girls when expressed as an absolute value (litres/min). Thus they appeared to be just as fit as their non-obese age-matched peers.
However when the aerobic performance was expressed as the maximum oxygen uptake per kilogram of body weight that had to be moved when running or walking then the obese subjects show a reduced performance of nearly 25% because of the extra weight of fat that they had to move.
A study of exercise performance was carried out in 17 obese girls and young adults. During submaximal steady-state bicycle exercise oxygen intake (Vo2) for a given work output was raised in obese subjects but minute ventilation at a fixed carbon dioxide output, gas exchange, blood gases, and cardiac output at a given VO2 were similar to the values previously found for normals. In obese subjects high levels of VO2 for fixed W were also obtained on the treadmill but when these were standardized for body weight (unlike the bicycle test) it was shown that the obese girls and women exercised within the normal (expected) range of aerobic energy expenditure.
During maximal performance the absolute VO2 max was the same in obese and nonobese subjects but for a given body weight, lean body mass, and leg muscle (plus) bone volume, VO2max was reduced by 23.8, 16.3, and 24.5% respectively, in the former group. It was concluded that obesity though having minimal affect on responses to submaximal exercise is nevertheless associated with a marked reduction in physiological performance at or near maximal effort.
This research study was designed and carried out by Professor Anthony J Sargeant as part of his PhD which was awarded by The Board of Studies in Physiology of London University in 1975. Using healthy normal subjects Tony Sargeant was able to show that large increases in the maximum oxygen uptake that could be achieved in one-leg exercise after one leg-training (consequent upon a direct training effect at the peripheral muscle level) were not reflected in two leg exercise maximum oxygen uptake where maximum cardiac output (which had not been subjected to training stimulus by the one-leg exercise) was the determining factor.
The effects of training resulting from one-leg exercise on a stationary bicycle ergometer have been studied. Seven subjects were habituated to one- and two-leg progressive exercise tests on 11 successive days and were then trained for 60 min-day-1 (30 min each leg) 3 times per wk for 5-6 wk at approximately 80% of their one-leg VO2 max. VE max increased (P less than 0.05) by approximately 14 1-min-1 and VO2 max by approximately 0.34 1-min-1 (+14%; P less than 0.05) in one-leg exercise. This latter increase was not, however, reflected in the two-leg VO2 max which only increased 145 ml-min-1 (4.7%). It was concluded that training is specific and in one-leg work the phenomenon is mainly peripheral in origin, but in two-leg work the limitation to maximal exercise is still provided by the capacity of the central cardiovascular system to transport oxygen to a given effective muscle mass.
Published in the prestigious medical research journal, Clinical Science, Professor Anthony J Sargeant carried out this research into rehabilitation therapy for young military personnel as part of his PhD which was completed while working for the Medical Research Council (UK). The data was collected at the Joint Services Medical Rehabilitation Unit in Chessington, Surrey, UK, over a period of about two years (1973-74). Tony Sargeant carried out the research working largely alone with occasional student assistance utilising a technique for examining the aerobic function of each leg individually – which technique he had previously developed on normal subjects when examining the limitations to maximum aerobic performance.
1. Eight patients who had suffered a fracture of one leg were studied before and after a 7 weeks period of rehabilitation during work with one leg and both legs on a bicycle ergometer.
2.In submaximal exercise minute ventilation for a given carbon dioxide output and tidal volume at a given minute ventilation remained unchanged throughout the period of therapy for both one- and two-leg exercise: oxygen intake for a given work output and cardiac frequency for a given oxygen intake decreased in both the injured and uninjured limb during one-leg work, although in two-leg exercise there was no significant change.
3. Oxygen intake at zero load was subtracted from the maximum oxygen intake measured during loaded exercise to give net values for each limb exercised separately or both legs exercised together. The net maximum oxygen intake thus calculated increased 8-9% (*17 1/min) in the uninjured leg and 17-4% (*29 1/min) in the injured leg during one-leg exercise. In two-leg exercise the increase was 17-2% (*43 1/min), which approximately equals the increase in the two legs measured separately.
4. In both legs there was an increase in leg muscle (plus bone) volume although this was significant in the injured leg only.
5. The maximum oxygen intake attained in two-leg exercise for a given leg volume in the patients at discharge was not significantly different from that found previously in a cross-sectional survey of young healthy (naval) servicemen. Thus the rehabilitation programme investigated appears to be effective, although the spontaneous recovery without a rehabilitation programme is unknown.