Title: The effect of individualising training intensities with. respect to the anaerobic threshold in the elderly.

Transcription

1 Title: The effect of individualising training intensities with respect to the anaerobic threshold in the elderly. Short Title: Training at the anaerobic threshold in the elderly. 1

2 Abstract: Aim: One of the most crucial problems in designing exercise programmes is making the prescription at the appropriate intensity. The aim of this review was to examine training interventions that have been carried out in the elderly in order to determine if using the anaerobic threshold is a safe way to prescribe an optimal intensity to induce beneficial adaptations and adherence to protocols in this population. Background: The anaerobic threshold is a measure of cardiorespiratory fitness. Many exercise prescriptions are based on a percentage of maximal oxygen consumption or max heart rate. However maximal testing can be risky in an elderly population and estimations of maximal heart rate can be inaccurate. Furthermore, if individuals are exercising at a relative percent of their max they may be exercising above or below their own anaerobic threshold. Therefore the stress induced is not uniform. Prescriptions based on VO 2max may not achieve the desired effect in all individuals, especially in an elderly population as the anaerobic threshold occurs at a higher percent of VO 2max and is more variable in the elderly. Therefore it is proposed that prescribing exercise based on the anaerobic threshold would be safer (as it can be measured during submaximal exercise) and more efficient in bringing about beneficial adaptations in an elderly population. Keywords: Aging, aerobic exercise, anaerobic threshold, training intensity, individualised programme. 2

3 Introduction: The number of people aged 65+ is the fasted growing segment of the population 1. Unfortunately age related loss of cardiorespiratory fitness leads to even daily activities becoming difficult. The resulting loss of mobility can lead to a loss of independence 2. Physical activity and fitness are also associated with a decreased rate of morbidity and all cause mortality 2. Participation in a regular exercise program is an effective intervention/ modality to reduce/prevent a number of functional declines associated with aging 3. Furthermore, the trainability of older individuals is evidenced by their ability to adapt and respond to both endurance and strength training. Few older adults participate in levels of physical activity that may benefit their health 4. Physical activity levels are similar for adults aged years, with a sharp decline from the age of 75 onwards 4. An increase in physical activity would increase the overall health of the elderly population. Thus it is important to establish the dose of activity that is needed to postpone the age related decline in cardiorespiratory fitness. Aerobic/endurance training can help to maintain and improve various aspects of cardiovascular function and health, as measured by maximal oxygen consumption (VO 2max) and cardiac output, as well as enhance submaximal endurance 1. One of the most crucial problems in designing exercise programmes is to make the prescription at the appropriate intensity. Exercise Prescription in the Elderly: To elicit a training effect an overload in the cardiovascular system is needed which for younger persons is usually at to moderate intensity 5. However elderly people are more deconditioned, fragile and susceptible to injury. The VO 2max is the level of oxygen consumed when he/she is exercising at his/her maximum. It is harder for elderly to reach this intensity of exercise. Therefore being unable to reach a VO 2max may result on prescriptions based on this method being less precise. Furthermore maximal exercise test are accompanied with a certain degree of risk such as myocardial infarction 6. Katch et al. 3

4 (1978) 7 studying normal healthy elderly subjects showed that at a preselected percentage of maximal heart rate (HRmax) individual subjects may exercise above or below their anaerobic threshold and thus exhibit dissimilar responses 8. Non individualised methods based on the relative percent concept make it difficult to evaluate a given individuals exercise stress. The anaerobic threshold (AT) differs among people as a function of age, gender, physical fitness, health etc. in such a way that training at the anaerobic threshold is individualised 9. In sedentary elderly the anaerobic threshold occurs at a higher percentage of VO 2max 10. Due to this exercise prescription based on % VO 2max in this population may underestimate the necessary stimulus for stimulating a training effect. Therefore in the elderly the anaerobic threshold may be a better way to prescribe exercise intensity in the elderly as it can be measure submaximally and evaluate the level of cardiorespiratory fitness 5. Anaerobic Threshold: During exercise the oxygen consumption above which aerobic energy consumption is supplemented by anaerobic mechanisms causing a sustained increase in lactate is termed the anaerobic threshold 11. The oxygen requirement is greater than the supply which increases anaerobic glycolysis for generation, converting pyruvate to lactate 12. The anaerobic threshold is commonly measured by either blood lactate or ventilatory gases 13. The anaerobic threshold can be measure directly from lactate concentration in the blood during an incremental exercise test of increasing intensities (when measured this way it is also termed the lactate threshold). The lactate threshold (LT) is the first significant/non linear increase in blood lactate above baseline 14,15. However gas exchange measurements made during exercise testing which can be used to non-invasively detect VO 2 at which the anaerobic threshold occurs. This is based on the increased carbon dioxide output which occurs with in association with acute metabolic acidosis 11 and is also called the ventilatory 4

5 threshold (VT). VCO 2 below the AT increases linearly with VO 2 as related to the metabolic respiratory quotient of the muscles 11. However above the AT the slope becomes steeper as VCO 2 increases relative to VO 2. The transition from the more shallow to the steep slope is the anaerobic threshold. This is the V- slope method of detecting the ventilatory threshold. The ventilatory equivalent method is based on the fact that the increase in VCO 2 is usually accompanied by an increase in ventilation (VE), however VO 2 remains linear. Therefore the ventilatory equivalent of oxygen (VE/VO 2) increases while the ventilatory equivalent of CO 2 (VE/VCO 2) does not increase. This is a specific indicator of metabolic acidosis 11. Methods: Search: A Pubmed search was run using the words ventilation threshold or anaerobic threshold or lactate threshold AND training. Limits were activated to include only studies with subjects aged 65+. This yielded 8 studies. An additional search was then run on the databases Scopus and Sportdiscus using the keywords anaerobic threshold AND training AND elderly. From this one more study was identified. The reference lists of the articles identified were then searched for additional studies. From this two more articles were selected. Inclusion: Some studies were eliminated immediately based on their title. Others were eliminated after the abstracts were read. Studies were included if they conducted a randomised control trial (RCT), clinical control trial (CCC) or a prospective study. The articles had to include a training intervention at the anaerobic threshold (AT) as measured by the lactate threshold (LT) or the ventilatory threshold (VT). Subjects involved in the study had to be elderly people who were apparently healthy. This resulted in a 5

6 total of 11 articles that were included in this review. The search strategy and results are presented in Figure 1. The characteristics of the included studies are outlined in Table 1. The anaerobic threshold training involved both continuous and interval training, including walking, jogging, cycling, recreational activities and circuit training. Studies involved comparisons of above and below lactate threshold training, continuous vs. intermittent, anaerobic threshold training vs. %heart rate reserve, aerobic training at anaerobic threshold compared to mental training, and anaerobic threshold arm cranking compared to leg cycling. 6

7 Figure 1 Flow chart of article selection process. Initial search of Pubmed, Scopus and Sportdiscus 475 articles retrieved for review 9 articles selected for inclusion 466 articles excluded based on title or abstract Reference lists reviewed and an additional 2 articles selected 11 articles included in review 7

8 Study No. of Participants Gender Belman & Gaesser male, (1991) female. Takeshima et al. 19 Male and (1993) 19 female Fabre et al. (1997) female, 6 male Motoyama et al male, (1998) female Ahmaidi et al. 22 Not (1998) 8 specified Fabre et al male, 27 (1999) 17 female Table 1 Characteristics of studies reviewed Average Age Allocation and Groupings Intervention Frequency and Duration 68 years 8 subjects from concurrent study served as control, 17 randomly allocated to high or low intensity intervention 69 years 11 intervention, 8 controlallocation not specified 64 years participants randomized into two groups: individual or standardised training 75 years 13 volunteered to take part in the exercise group so 13 age and sex matched controls were used 63 years Randomly assigned to control or intervention. 66 years Randomly allocated into aerobic training, mental training, aerobic plus mental training and control 30mins low intensity or high intensity walking. Low intensity below LT, high intensity above LT. 30 mins cycling at watts at LT followed by 30 mins recreational activities at HRLT Interval walking at individual HRVT or standardised 50% HRr Treadmill training at LT intensity for 30 mins Interval walking/jogging at HRVT interspersed with 1 min active recovery (20 bpm below HRVT) 1 hour interval training at HRVT. Total time spent at HRVT slowly increased. 4 X weekly for 8 weeks 2-3 X weekly for 12 weeks 2 X weekly for 12 weeks 3-6 tx weekly for 36 weeks 2 X weekly for 12 weeks 2 X weekly for 8 weeks 8

9 Study No. of Participants Gender Fabre et al male, 27 (2002) 20 female Takeshima et al male, 20 (2004) 16 female Average Age Pogliaghi et al. 18 Male 69 +/- 5 (2006) 18 years Lepretre et al male, 19 (2009) 22 female Allocation and Groupings Intervention Frequency and Duration 65 years Randomly allocated into aerobic training, mental training, aerobic plus mental training and control 68 years randomly assigned into control and intervention 12 participants randomly assigned into two intervention groups of either arm cranking or leg cycling. 6 control participants unwilling to participate in intervention 1 hour Interval training at HRVT. Total time spent at HRVT slowly increased. 30 mins concurrant circuit style aerobic and resistance programme performed at HRLT 30 mins continuous exercise at HRVT in either arm cranking or leg cycling 65 years All included in intervention 6 X 4-min interval walking/jogging at the first ventilatory threshold alternated with 1-min at the second ventilatory threshold Riedl et al. 7 Male 64 years All included in intervention. 60 min cycle ergometer training at (2010) 21 working corresponding to LT 2 X weekly for 8 weeks 3 X Weekly for 12 weeks 3 X Weekly for 12 weeks 2 X weekly for 9 weeks 5 X weekly for 6 weeks Table 1 Continued. HRLT= heart rate at lactate threshold, HRr= heart rate reserve, HRVT= heart rate corresponding to ventilatory threshold, LT= lactate threshohld. 9

10 Effectiveness of anaerobic threshold training: Maximal Oxygen Uptake (VO 2max) VO 2max is the single best measure of cardiorespiratory endurance 16. However as it is difficult for elderly subject to achieve VO 2max some studies evaluated VO 2peak instead for the subjects who did not obtain the max. An increase in VO 2peak represents improvements on cardiorespiratory endurance and aerobic exercise capacity. In this review when an improvement in aerobic exercise capacity (i.e. VO 2max or VO 2peak) is being discussed VO 2peak will be the term used. Of the 11 studies in this review 10 used VO 2peak as an outcome measure. Both the cycle ergometer and treadmill were used to perform graded exercise tests during which gas exchange was directly measured in order to determine VO 2peak. All ten studies noted a significant improvement in VO 2peak after the intervention. Improvements ranged from %. The age-related decline in VO 2peak is important to reduce because if the VO 2peak becomes too low it will not be possible to maintain independent living. The % increase in Vo 2peak shows that exercising at the anaerobic threshold can help prevent the decline in aerobic capacity associated with age. Anaerobic Threshold Changes that occur at the AT could be more meaningful to the elderly than the VO 2peak itself as daily activities rarely require maximal effort 17. All eleven studies reported an improvement in at least one parameter measured at the anaerobic threshold; however the outcome measures were varied. Five of the studies measured VO 2 at either the lactate or ventilatory threshold and found it to be increased 8,9,16,18,19. Values varied from % which were higher values than the increase in VO 2max. The average increase was 22%. Further evidence of the improvement of cardiorespiratory fitness is provided by the increase in VO 2 at the anaerobic threshold (VO 2 AT). The increase in VO 2 AT has 10

11 been suggested to be due to increased oxygen delivery and blood lactate removal. The resulting increase in VO 2 AT should allow older adults to engage in sustained rigorous work for longer periods of time 16. Four studies 17, 20, 21, 22 found that the AT increased as a % VO 2max. This increase ranged from %. Takeshima et al. (1993) 19 noted that the % VO 2max at the lactate threshold tended to be higher but did not reach a statistically significant difference. Pogliaghi et al. (2006) 18 and Lepretre et al. (2009) 22 both found an increased power output at the VT while Motoyama et al. (1998) 23 found a 9.8% increase in speed at the LT. Lepretre et al. (2009) 23 was the only study to measure blood lactate at the same absolute intensity and found that it was reduced after training by 39.7%. This suggests that higher intensities of exercise can be tolerated before the onset of blood lactate accumulation. This is supported by the significant increase in the total exercise time of the graded exercise test found by Belman & Gaesser (1991) 24. These improvements at the AT suggest a greater submaximal exercise tolerance. This improved submaximal fitness improvements will allow the elderly to continue exercising and also help with daily activities. Ventilation and Heart Rate: Seven of the eleven studies measured improvement in either ventilation or heart rate (HR). Ahmaidi et al. (1998) found that minute ventilation (VE) and HR were reduced at the pre-training VO 2peak. Similarly Fabre et al. (1997) 9 found that HR and VE were reduced at 60, 80 and 100% of the pre-training VO 2peak. Belman & Gaesser (1991) 24 found an 11.75% reduction in VE and 6-8% reduction in HR at the same submaximal intensity, while Pogliaghi et al. (2006) 18 only found a decrease in HR at the same submaximal intensity. These reductions in HR and VE demonstrate that improved exercise tolerance can occur as a result of training at the AT. Increases in peak VE 18, 22 were also found. Functional Improvements: 11

12 Five of the studies used different measure of functional outcomes. Takeshima et al. (2004) 16 increased knee flexion strength by 76%, Takeshima et al. (1993) 19 increased leg extensor power by 14.3% while Lepretre et al. (2009) 22 increased max tolerated power by 18.9%. These improvements in strength and power may help in the prevention of falling as well as the ease of functional tasks such as getting out of a chair or climbing the stairs. Fabre et al. (1997) 9 and Motoyama et al. (1998) 23 both found a significant increase in walking speed at the AT. Furthermore Fabre et al. (1999) 17 found that there were significant changes in the category of functional life in The Subjective Quality of Life Profile. In this study the two groups that completed AT training significantly improved values such as fitness, dyspnoea and tiredness. Also their degree of satisfaction was greater than the control group. Body Composition: Only two of the eleven studies found improvements in body composition post AT training. Takeshima et al. (2004) 16 found that body fat as measured by skinfolds decreased by 16%. Skinfolds is an estimation of subcutaneous adiposity. Arm and thigh girth did not decrease which suggests a gain of lean mass. Riedl et al. (2010) 21 found that 6 week LT training decreased subscapular skinfolds by 24% and body fat by 9.9%. Lipid Profile: In sedentary humans, advancing age is associated with unfavorable changes in plasma lipid and lipoprotein levels 1. The most consistent effect of regular aerobic exercise on plasma lipoprotein levels is an increase in the cardioprotective high density lipoprotein-cholesterol levels 1. Cholesterol increases with age and aerobic training can enhance glycemic control as well as improving lipid profile in older adults 21. Three of the eleven studies took blood lipid measurements. All three found significant improvements after AT training. Takeshima et al. (2004) 16 and Riedl et al. (2010) 21 significantly increased 12

13 high density lipoprotein levels thus improving the lipid profile by reducing the LDL-C: HDL-C ratio. Takeshima et al. (1993) 19 reduced total cholesterol by 4.25% and triglycerides by 11%. Blood Pressure: Hypertension is an established independent risk factor for coronary heart disease, stroke, and cardiovascular disease and is more prevalent in people aged 60 and over 23. Two of the studies recorded reduced blood pressure measurements after AT training. Lepretre et al. (2009) 22 found that systolic blood pressure was reduced by 5.5% while Motoyama et al. (1999) 23 found 9.99% decrease in systolic blood pressure and 10.6% decrease in diastolic blood pressure. Memory: Cognitive function decreases with aging 20. This decline in mental functioning may be decreased with physical activity. Cerebral blood flow decreases with aging which may induce the decrease in cognitive function. Aerobic training has the potential to reduce this decrease in cerebral blood flow 20. Fabre et al. (2002) 20 found that training at the AT twice weekly for two months increased memory quotient by 8.5% in the Scale of Wechsler and also significantly increased paired associates learning and logical memory immediate recall. There was no difference in the control group so these changes can be attributed to the AT training. It has been postulated that there is a possible increase in norepinephrine and serotonin due to aerobic training which is responsible for mnesic mechanisms 20. Discussion: The objective of exercise prescription in the elderly is to maximise safety, efficiency and compliance. Prescribing an appropriate intensity is crucial in obtaining these objectives. If the intensity is too high there is increased risk of injury or accident due to the frailty of elderly people. Also they will be less likely 13

14 to maintain the exercise habitually if they find it too hard. However if the exercise intensity is too low it may not elicit the required overload in order to be beneficial. Exercise intensity based on relative intensity may have limited usefulness in ensuring that a desired level of metabolic stress is utilised for all subjects. Even if subjects are exercising at the same %VO 2max the metabolic stress using metabolic acidosis as the criterion is not constant among all subjects 19. The anaerobic threshold takes into account specific levels of stress needed in order to see improvements. Therefore it takes better into account an individual s capacity for exercise. As it can be measured submaximally it is also associated with less risk than the VO 2max which is very important in this population. This review shows that training at the AT is an effective way to improve both maximal and submaximal exercise capacity in the elderly. Increases in a wide range of outcome measures are evident which suggests increased functional capacity and performance in the elderly. It is also safe as no injuries were obtained during any of the AT training interventions. Many of the studies also noted high compliance rates to the training interventions. Although positive improvements in VO 2peak, anaerobic threshold, functional capacity and tolerance for submaximal exercise were observed the improvements were quite variable. The discrepancies could be due to the duration, frequency and mode of training utilised in the studies. It must be noted that the interventions that utilised continuous exercise did not appear to elicit as high improvements as the training programmes that implement interval training. The average increase in VO 2max was 8% in the continuous training programmes while it was 17% in the studies that utilised interval training. This could be because the interval trainings were progressed in such a way that the time spent at the AT was increased and the active recovery time was reduced while the duration and intensity of the continuous programmes were held constant. It does appear that interval training seems to be more effective. Makrides et al. (1990) 25 showed a 38% increase in peak O2 with interval training consisting of repeated 5-min bouts of high-intensity exercise (140 bpm, 85% of peak VO2) separated by recovery periods at a 14

15 lower intensity (65% of peak VO2). A possible direction for future research would be to compare the effects of interval training and continuous training at the lactate threshold in the elderly. Although it is evident from the research that has been done that there are many positive short term benefits for the elderly from training at the AT such as improved cardiorespiratory function, tolerance to submaximal exercise, reduced blood pressure and cholesterol as well as improved cognitive ability there is a lack of longitudinal studies examining the long term benefits of adhering to exercise at this intensity for this population. It is possible that there are associated reduced rates of disease and mortality but has not yet been investigated. Although Fabre et al. (1997) 9 demonstrated a better adaption of variables with an individualised training programme based on HR at the VT compared to HR based on % Heart rate reserve there are drawbacks with this method. It requires adequate knowledge and experience to be able to determine the anaerobic threshold whether by LT or VT. It is also more time consuming than estimation of HRmax (220-age). Therefore it may not be more difficult to implement on a wider scale than standardised training intensities. However where possible individualised training programmes based on the anaerobic threshold can ensure that a safe and adequate amount of stress is achieved in order to elicit beneficial adaptations in an elderly population. 15

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