Exercise studies with elderly volunteers

Exercise studies with elderly volunteers

C.A. Greig

The practicalities of conducting exercise studies with elderly and very elderly people have not been well described. In order to help others plan and perform such studies we describe our experience of recruiting volunteers, applying selection criteria, measuring strength, power, cardiorespiratory responses, and potentially related functional abilities.

Exclusion criteria are offered, for safety and to characterize subjects as free of disease which might alter their exercise performance. International agreement on these, or similar, criteria would be valuable.

The budget must be adequate for prolonged recruitment before a study and for the liberal use of taxis during it.

With healthy subjects in their seventies, the coefficients of variation (CV) for repeated measurements of strength and power were: handgrip 3%, isometric knee extension 6%, isometric elbow flexion 6%, and lower limb extensor power 9%. CV for isometric knee extension by healthy subjects in their eighties was 4%. Treadmill ergometry is more time-consuming than with younger subjects. During progressive treadmill tests, the heart rate interpolated to oxygen consumptions of 10 and 15 ml.[kg.sub.-1].[min.sub.-1] had CV = 4% and 7%, respectively.

Regular physical activity has an important role in preventing disease (e.g. osteoporosis, coronary artery disease, non-insulin dependent diabetes mellitus), in reducing disability (e.g. angina, intermittent claudication, chronic airflow obstruction) and in enhancing mood and general well-being (1). It may also preserve the ability to perform functionally important everyday tasks (2) despite the progressive loss of muscle mass associated with old age (3)(4). Knowledge of exercise physiology in old age, however, is sketchy, especially beyond 75 years of age. This paper describes our experience of some of the difficulties presented by such studies, and potential solutions in respect of recruitment, selection, safety, and test protocols.

During the past 3 years, the Human Performance Laboratory (HPL) has recruited over 950 volunteers between the ages of 62 and 98 years. By May 1993, tests of muscle strength and explosive power and related tests of functional ability had been performed on 350 occasions by 249 volunteers aged 62-98 years (Table I) and 126 treadmill exercise tests and 90 self-paced corridor walking tests had been performed by 34 volunteers aged 65-84 years (Table II).

Table I. Tests of strength, power, and poetntially related functional abilities performed in the HPL, to May 1993 (189 women and 60 men; age range 62-98 years)

Age group No. of No. of

(years) people occasions

60-69 36 51

70-79 112 166

80-89 89 119

90 + 12 14

Total 249 350

Table II. Treadmill exercise tests and/or corridor walking tests performed in the HPL, to May 1993 (23 women and 11 men; age range 65-84)

Age group No. of No. of

(years) people occasions

60-69 4 17

70-79 22 91

80 + 8 40

Total 34 148

Recruitment of volunteers

This is an important and largely unpublicized issue. Recruitment is extremely time consuming, particularly when applying strict health criteria to people over 75. Not only is pathology common at that age but it has been suggested that healthy elderly people may be less inclined to volunteer for studies in a ‘clinical’ environment (5).

To attract healthy volunteers over 65 we published a prominent advertisement in a local newspaper and posters were displayed around the hospital, in local day centres, shops and luncheon clubs. The response was disappointing. A ‘press release’ was then sent to a selection of both national and local newspapers. This resulted in several published articles, often quoting our press release verbatim, and produced a large response. The majority of the potential volunteers now on the HPL’s register were identified in this way.

Although newspaper articles have proved to be our most successful means of attracting volunteers, the proportion of volunteers who meet our selection criteria is low. For example, out of 225 responses to a recent article in a London daily newspaper, only 22 were suitable for inclusion in our studies. Of a total of 585 responses to one series of local and national newspaper articles, only 17% were suitable for inclusion.

One of our studies required volunteers aged over 75 who, although ‘healthy’ or ‘medically stable’ (see ‘Selection of subjects’, below), were sufficiently frail that they had chosen to live in warden-controlled accommodation. First, permission was obtained from local housing trusts providing such accommodation. The wardens then broached the subject with those they considered potential volunteers. Only then did the investigator approach the potential volunteers, in their homes and accompanied by the warden. It is hard to see how this slow process could have been accelerated without either taking advantage of the residents or antagonizing the management. Recruiting this type of subject remains a challenge.

Although selection of our volunteers has been on the basis of health, not fitness or habitual physical activity, it is possible that our methods of recruitment may preferentially attract those with a personal interest in physical activity. This remains a concern.

Selection of subjects

All studies of human ageing are faced with the problem of defining ‘normality’ in a population with a high prevalence of chronic disease. In old age, ‘usual’ and ‘normal’ are no longer synonymous. In order to study the effects of ageing, and to provide reference values against which to judge data from elderly patients, disease-free subjects must be selected. This requires tightly defined, pre-determined criteria. The SENIEUR protocol (6)(7) was developed to identify healthy subjects for immunological studies but is not ideal for exercise studies. Our exclusion criteria were designed both for safety and to define degrees of freedom from diseases which might alter exercise performance (Tables III and IV). Internationally agreed criteria for the selection of subjects for exercise studies would be valuable. Perhaps ours can be a first step in that direction.

Table III. Exclusion criteria to define ‘healthy’ (i.e. ‘diseasefree’) elderly subjects for exercise studies

History of myocardial infarction within the previous 10

years

Cardiac illness: e.g. symptoms of aortic stenosis, acute

pericarditis, acute myocarditis, aneurysm, severe angina,

clinically significant valvular disease, uncontrolled

dysrrhythmia, claudication, within the previous 10 years

Thrombophlebitis or pulmonary embolus within the

previous 10 years

History of cerebrovascular disease

Acute febrile illness within the previous 6 months

Moderate or severe airflow obstruction

Metabolic disease (e.g. diabetes, thyroid disease), whether

controlled or uncontrolled

Major systemic disease diagnosed or active within the

previous 20 years (e.g. cancer, rheumatoid arthritis)

Significant emotional distress, psychotic illness or anything

worse than mild anxiety or depression within the previous

10 years

Osteoarthritis, classified by inability to perform maximal

contractions of upper and lower limbs without pain

Bone fracture sustained within the previous 2 years

‘Old person’s fracture’ after 40 years of age (wrist, hip,

vertebral)

Non-arthroscopic joint surgery, ever, in the relevant limb

part

Any reason for a loss of mobility for greater than 1 week in

the previous 6 months or greater than 2 weeks in the

previous year

On daily medication (including daily simple analgesia); on

oestrogen replacement therapy; on medication for

hypertension, or with a diuretic for any other reason, even

if not daily

Obese, i.e. a Quetelet index (wt.[ht.sup.-2]) greater than 29.9

Resting systolic blood pressure > 200 mmHg, or resting

diastolic blood pressure > 100 mmHg

Table IV. Exclusion criteria to define ‘medically stable’ elderly subjects for exercise studies

History of myocardial infarction within the previous 2 years

Cardiac illness: symptoms of aortic stenosis, acute

pericarditis, acute myocarditis, aneurysm, severe angina,

clinically significant valvular disease, uncontrolled

dysrrhythmia, claudication, within the previous 10 years

Thrombophlebitis or pulmonary embolus within the

previous 2 years

History of cerebrovascular disease

Acute febrile illness within the previous 3 months

Severe airflow obstruction

Uncontrolled metabolic disease (e.g. diabetes, thyroid

disease)

Major systemic disease active within the previous 2 years

(e.g. cancer, rheumatoid arthritis)

Significant emotional distress, psychotic illness or

depression within the previous 2 years

Lower limb arthritis, classified by inability to perform

maximal contractions of lower limbs without pain

Lower limb fracture sustained within the previous 2 years;

upper limb fracture sustained within the previous 6

months; non-arthroscopic lower limb joint surgery within

the previous 2 years

Any reason for a loss of mobility for greater than 1 week in

the previous 2 months or greater than 2 weeks in the

previous 6 months

Resting systolic blood pressure > 200 mmHg or resting

diastolic blood pressure > 100 mmHg

Taking beta-blockers or digoxin, or not in sinus rhythm

(excluded from ergometry because of difficulty

interpreting heart rate)

On daily analgesia

Volunteers are sent a health questionnaire to test whether they meet our criteria. Those not excluded by their responses to the questionnaire are invited to the HPL where the exclusion criteria relating to blood pressure, height and weight are applied. For those taking thyroid replacement treatment, eligibility for classification as ‘medically stable’ (Table IV) is then verified by measuring thyroid-stimulating hormone in venous blood.

‘Laboratory’ studies

Despite the health and enthusiasm of our volunteers, we found that taxis were frequently required, to maintain co-operation and to avoid fatigue. This has proved expensive, especially in a training study which involved a weekly exercise class (8).

Strength and power: The maximum voluntary isometric strength of the knee extensors (9)(10), elbow flexors (10) and handgrip (Takei Kiki Kogyo, Japan) can be measured in healthy elderly people, by standard methods, with repeatability comparable with that found with younger subjects (Table V). The completeness of activation of the quadriceps in voluntary contractions can be checked with the twitch superimposition technique (11)(12) modified for use in large muscles (13)(14); this has been well tolerated by our subjects.

Table V. Strength and power: repeatability of measurements made on different days in healthy people in their 8th decade (n = 12, median age 74, range 70-77 years) and in their 9th decade (n = 12, median age 82, range 80-87 years): measurements are for the side which was stronger on the first test occasion

Coefficient of variation(*)

8th decade 9th decade

Isometric strength([dagger])

Knee extension 5.9 3.8

Elbow flexion 5.9

Handgrip 2.9

Explosive power([double dagger])

Lower limb extension 8.6

(*)[square root]([sigma][d.sup.2]/2N) x 100/X, where d = difference between paired measurements, N = number of pairs, and X = grand mean.

([dagger])Best of [greater than or equal to] 3 efforts.

([double dagger])Best of [greater than or equal to] 5 efforts.

The explosive power of the lower limb extensors is measured with a modified version (15) of an instrument (16) which records the acceleration imparted to a heavy flywheel by a single thrust of the seated subject’s lower limb, permitting the safe measurement of explosive power without the need for vertical leaps or upstairs sprints. Again, repeatability is comparable with that seen with younger subjects (Table V). This instrument is even suitable for use with very frail patients, although we have had to place it beside wall-mounted handrails to facilitate transfers on and off.

Cardiopulmonary exercise testing: The treadmill has been the ergometer of choice in our studies with healthy elderly people. Walking is a familiar activity and we have assumed that it might relate better than cycling to everyday life. Nevertheless, the treadmill is a large unfamiliar piece of equipment, noisy and potentially intimidating. The subject cannot stop walking at will, may even forget to walk if distracted, and may have difficulty balancing on the moving belt. It is possible that older subjects may grip the front or side-rails of the treadmill, rather than merely resting their hands lightly on the rails, potentially affecting oxygen intake, heart-rate, and blood pressure.

Subjects often experience problems wearing a mouthpiece and this had led to tests being stopped prematurely. We do not know why our elderly subjects find the mouthpiece so difficult. It is not simply a question of whether or not they have false teeth, although these can add to the problem. Presumably the discomfort results from both reduced elasticity of oral soft-tissues and gingival recession. In an attempt to resolve this, the most difficult aspect of cardiopulmonary testing in this age group, time is given before the test to practise inserting a spare mouthpiece, not connected to the gas analysers.

Safety: Treadmill tests require two investigators, and for the first test we require one to be medically qualified. All non-medical investigators receive instruction and 3-monthly updating in cardiopulmonary resuscitation (CPR) from the hospital’s Resuscitation Officer. The laboratory is equipped with a semi-automatic defibrillator and is clearly signposted for the hospital’s cardiac arrest team. The treadmill (P. K. Morgan) has an overhead gantry, front and side-rails. The volunteer performs the test wearing a harness attached to a trip switch on the gantry.

The subject’s resting blood pressure and 12-lead electrocardiogram (ECG) are recorded. Then, after explanation, demonstration and familiarization, they perform their first submaximal progressive exercise test, without a mouthpiece and following the conventional Naughton protocol (17). The ECG is monitored continuously and blood pressure is measured during each 3-minute stage. The test is halted if (i) the subject requests it, (ii) the ECG shows [greater than or equal to] 0.2 mV of ST depression or elevation, coupled ventricular extrasystoles, [greater than or equal to] 10 ventricular extrasystoles per minute, extrasystoles approaching R on T, (iii) blood pressure fails to rise with increasing work rate, or (iv) the subject develops pallor with sweating, chest pain, undue breathlessness or other evidence of intolerance of exercise. ECG monitoring is also used throughout all subsequent progressive treadmill tests. Of a total of 58 such tests, only one has been stopped, owing to the subject developing an increasing number of ventricular ectopic beats.

Choice of test protocol: It seemed unwise to use truly maximal exercise tests until we had acquired substantial experience in exercise testing elderly people. To date, therefore, we have used a protocol in which the test is stopped when the subject reaches 70% of their predicted maximum heart-rate, calculated as 70% of (210 — 0.65 x age in years) (18). The first test usually follows the conventional Naughton protocol (17). Thereafter, a suitable protocol must strike a compromise among the following three conditions: (1) The protocol must be such that, despite a rather low maximum work rate, the elderly person can complete a sufficient number of stages adequately to characterize their response to submaximal exercise, in particular the relationship of heart rate and ventilation to oxygen intake. (2) Since the majority of elderly volunteers experience difficulty wearing a mouthpiece, the total duration of the test must be kept to a minimum. (3) Each stage should be long enough to allow achievement of a ‘steady-state’ condition with respect to the variable of greatest interest. Our current protocols (Tables VI and VII) were based on the Naughton protocol with these three criteria in mind. (The increments in work rate are sufficiently small for the heart rate not to differ between the first and fourth 15s periods of the second minute of each 2-minute stage.) Occasionally, however, further modification may be necessary for individual subjects. With these protocols, repeated tests with healthy elderly subjects (four women and three men, mean age 76, range 73-80) gave reproducible results for heart rate interpolated to oxygen consumptions of 10 and 15 ml[multiplied by][kg.sup.-1][multiplied by][min.sup.-1], viz. coefficients of variation of 4.4% and 6.6%, respectively. The slope of the heart rate versus oxygen consumption relationship was less securely identified (coefficient of variation = 22%).

Table VI. Treadmill protocol for elderly subjects who had previously managed more than five stages of the Naughton protocol

Duration Speed Elevation

Stage (min) (km[multiplied by][h.sup.-1]) (degrees)

1 2 1.5 0

2 2 3 0

3 3 3 2

4 3 3 4

5 3 3 6

6 3 3 8

7 3 3 10

Table VII. Treadmill protocol for elderly subjects who had previously managed five or fewer stages of the Naughton protocol

Duration Speed Elevation

Stage (min) (km[multiplied by][h.sup.-1]) (degrees)

1 2 1.5 0

2 2 3 0

3 2 3 1

4 2 3 2

5 2 3 3

6 2 3 4

7 2 3 5

8 2 3 6

9 2 3 7

10 2 3 8

‘Functional’ tests

Strength, power and cardiorespiratory responses during treadmill ergometry do not correspond perfectly with the results of tests of everyday functional ability. It is not enough to make ‘laboratory’ measurements. They should be coupled with measurements of corresponding everyday tasks.

Strength and power: Direct measurements of functional ability used in our studies include step height, the ability to rise from a 42 cm stool, and the ability to raise a weighted bag on to a 72 cm table (19)(20)(21). In healthy elderly people, the associations between rising from a chair or stepping ability and quadriceps strength or lower limb extensor power have not been clear cut (19), (21)(22), although, in the presence of pathology, others have shown reasonably strong associations between functional abilities and both strength (23) and power (24).

Cardiopulmonary exercise testing: It is usually assumed that data obtained from laboratory-based treadmill tests, after initial habituation, give a valid indication of the cardiorespiratory responses in everyday physical activity. It seems that this is not always the case with older subjects. Twelve healthy elderly subjects (71-80 years) had a significantly higher heart-rate during treadmill walking than during corridor walking at the same speed. This difference increased when a mouthpiece was worn on the treadmill and persisted after repeated testing: 12 healthy younger subjects (21-37 years) did not have higher heart-rates on the treadmill, either with or without a mouthpiece (25).

Traditional methods of ergometry must, therefore, be supplemented by tests which may describe an elderly person’s cardiorespiratory responses to everyday activity more adequately. Presumably such tests will be based on telemetric recordings of cardiorespiratory variables during free walking (25)(26). The 2-, 6-, or 12-minute walking tests (27)(28) may also prove appropriate.

Acknowledgements

We are grateful for the support that this work has received from the Violet M. Richards Charity Trust, the Peter Samuel Royal Free Fund, the British Geriatrics Society (Dhole Bursary), and Research into Ageing. We thank Ms G. Wynne RGN, Ms S. Jordan RGN, Dr S. Davies and Dr N. Uren of the Department of Cardiology for considerable assistance with our safety measures, and our volunteers for their cheerful and patient participation.

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Received 11 June 1993

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