**5. The exercise dose-response**

To be comparable across studies and to better determine the most efficacious exercise plan for promoting successful brain aging, researchers and clinicians need to attend to the multifaceted nature of the exercise prescription, or dosing, components. These components can be manipulated in a variety of ways so as to not only meet the research needs but also ensure that the participants will stick with the program. While not everyone is going to love to exercise, the exercise program should be designed to accommodate one's abilities, interests, and health status. Note that the exercise prescription is individualized not as a function of age or gender per se, but rather, it is individualized as a function of personal interests and health-fitness limitations. For research, the trick is to create a general exercise prescription for an entire group while maintaining an individualistic approach, to ensure the safety of each participant, prevent drop-outs, yet still be efficacious for the research goal. That is the "art" of an exercise prescription.

#### **5.1 Components of an exercise prescription**

When exercise is being used as a research tool, neurobiology researchers should consider the **FITT + P** paradigm (frequency, intensity, time, type, progression) of an exercise prescription recommended by the American College of Sports Medicine (ACSM, 2009). Precisely identifying each of these components within an exercise neurobiology study makes comparison across studies, replication of results, and advancement of the exercise science of neurobiology much more accurate. Furthermore, it makes providing global recommendations to the public easy. Vaguely described exercise protocols are one of the major pitfalls encountered in the neurobiological literature utilizing exercise as a treatment modality. Often the research outcomes are either un-interpretable or non-generalizable. Manipulation of any one of the five components in the FITT + P paradigm can alter the intervention outcome significantly, and varying more than one component within a study

must be done carefully. Ultimately the goal is to determine what type(s) of exercise recommendation(s) will best facilitate brain health maintenance. Reproducibility of the exercise prescription is paramount so that the findings can be applied across various physical activities and different populations.

### **5.1.1 Frequency ("F") of exercise**

232 Neuroimaging – Cognitive and Clinical Neuroscience

likely due to time, facility limitations, and monetary constraints. However, care must be taken when reporting the results from cross-sectional studies. Regardless of the strength of the associations, results should not be reported in such a way as to infer causation. Cross-sectional research has pointed the way towards the need for more controlled, randomized longitudinal outcome studies which can take the significant associations one step further and determine causation of an intervention. While acute outcome studies are able to state how exercise stresses the brain on an immediate basis, only longitudinal outcome studies will be able to recommend more definitive exercise dosing guidelines for maintaining and/or improving brain health over a lifetime. Even then, the recommendations will likely be for specific populations, a specific gender, or specific types of physical activity. It will take several years to arrive at the more global health fitness recommendations now common in the cardiovascular literature. There is plenty of work ahead for innovative exercise-focused neuroscientists.

The biggest blunder that has been occurring with the current brain studies is the pseudoscience reporting in the popular press. When public dollars are funding the research, it is important to get the science results out to the public in a media format that is understandable for the layman. However, the information is often unwittingly misrepresented by the media, resulting in conflicting reports when different modalities/populations are investigated, or worse, the media report leaves the impression that brain researchers are somehow privy to reading someone's mind. In the exercise neuroscience field, media interviews with researchers who are not trained in the exercise sciences or knowledgeable in the exercise design of a study has resulted in less than accurate interpretations of the study's purpose, strengths and/or weaknesses. This can have a dampening effect on future exercise neuroscience studies and may lessen the scientific integrity of the research itself. Thus it is critical that researchers understand the basics of the

To be comparable across studies and to better determine the most efficacious exercise plan for promoting successful brain aging, researchers and clinicians need to attend to the multifaceted nature of the exercise prescription, or dosing, components. These components can be manipulated in a variety of ways so as to not only meet the research needs but also ensure that the participants will stick with the program. While not everyone is going to love to exercise, the exercise program should be designed to accommodate one's abilities, interests, and health status. Note that the exercise prescription is individualized not as a function of age or gender per se, but rather, it is individualized as a function of personal interests and health-fitness limitations. For research, the trick is to create a general exercise prescription for an entire group while maintaining an individualistic approach, to ensure the safety of each participant, prevent drop-outs, yet still be efficacious for the research goal. That is the

When exercise is being used as a research tool, neurobiology researchers should consider the **FITT + P** paradigm (frequency, intensity, time, type, progression) of an exercise prescription

modality being used – in this case, exercise is the modality.

**5. The exercise dose-response** 

"art" of an exercise prescription.

**5.1 Components of an exercise prescription** 

**4. Media releases** 

How "often" one exercises is a critical component of the exercise dose-response. It depends not only upon the health status of the individual, but also the type (or modality) of exercise. To improve cardiovascular health (or aerobic fitness), metabolic and lipid profiles, and body composition, 3 days per week is the recommended minimum number of times one should exercise (ACSM, 2009). However, if a person is at either extreme of the physical fitness continuum, (i.e., extremely deconditioned/inactive versus highly fit/active), then multiple daily sessions of very short duration (i.e. time) or nearly daily sessions of moderately long sessions may be instituted. Hence, there is a distinct relationship between frequency of exercise and duration of exercise. Simply put, the amount of time (in minutes) one should expend in a given exercise session is partially determined by how frequently one is exercising on a daily or weekly basis. Furthermore, the 3-days-per week minimum recommendation only applies to aerobic conditioning. Strength conditioning should be performed 2-3 days per week with the goal to alternate muscle groups being trained, and flexibility training recommendations is a minimum of 2 days weekly. Fitting all three of these exercise components (aerobics, strength, flexibility) into one exercise session can cause an exercise session to require at least one hour of time. Therefore, it is common to break up the exercise program into "aerobic" training days and "strength/flexibility" training days, resulting in exercising almost daily.

#### **5.1.2 Intensity ("I") of exercise**

How "hard" one exercises has many physiological parameters to consider including heart rate response, perception of effort, and workloads on various types of equipment. All of these factors contribute to the "intensity" of the exercise prescription and are manipulated according to the desired outcomes (Nieman, 2010).

#### **5.1.2.1 Heart rate**

If aerobic conditioning is desired, then the recommendation is for one to exercise within a ""stimulus zone". This zone is based upon one's health status and a percentage of one's agepredicted maximum heart rate (220 - age). For the average individual, a "moderate" intensity stimulus zone is recommended. As can be seen in *Table 1*, a moderate heart rate stimulus zone would be 64 – 76% of one's maximal predicted heart rate. So if one is 50 years old, the predicted maximal heart would be 170, and the heart rate training stimulus zone would be 109 to 129 bpm.


MRI Techniques to Evaluate Exercise Impact on the Aging Human Brain 235

instructions as to how to set the speed and percent grade; if using a cycle ergometer, the exerciser would need to know how to set the resistance and at what speed to pedal. Sometimes this is determined by an entry exercise test and the settings are based upon a percentage of their max test results; other times it is arbitrarily determined and governed simply by determining a "comfortable" pace in order to attain a desired heart rate or RPE range. Using the latter method will enable the researcher to permit the exerciser to exercise on a greater variety of equipment, thereby helping to reduce exercise boredom and dropping out of a study. However, a word of caution: if the goal of the research is to determine the impact of a certain TYPE of exercise on the brain over a certain period of time, then the researcher must give explicit instructions as to which equipment use is permissible for exercise research participation. Sometimes, giving a research volunteer too many choices can truly confound interpretation of the research results. Thus, while that new exercise club down the road may be convenient and affordable for the study, the researcher must determine how precisely the exercise prescription must be adhered to and consider the

The first "T" of the FITT + P paradigm is Time. How "long" one exercises, or how much time is required to achieve a desired fitness benefit, depends upon one's health status and/or fitness goals, and as stated above, the frequency of exercise. If one is very deconditioned, then multiple sessions of brief duration may be recommended. These brief durations may be as little as 5 minutes. It is common for those with a fragile health status or simply deconditioned due to inactivity (but otherwise considered healthy) to be given an intermittent exercise prescription consisting of 5 minutes of physical activity interspersed with an equal amount of rest, with that dose repeated twice more in succession so that an equivalent of 15 minutes can be accrued. As one successfully adapts to the exercise stimulus, the rest sessions will be reduced so that eventually the previously deconditioned person can exercise for 15 continuous minutes. Once a baseline level of aerobic endurance is attained, then strength conditioning can be safely and effectively added to the exercise program. As indicated above, an exercise session focusing only on aerobic conditioning can require 15 to 30+ minutes. A strength conditioning program may also require 30+ minutes if the entire body is to be trained in one session. Flexibility training can be a stand-alone program or be incorporated into the regular exercise program as part of a warm-up and/or cool-down routine. Thus, flexibility training can take as little as 5 minutes or as long as 30 minutes,

While any one component of an exercise program may eventually take about 30+ minutes, it is standard to also incorporate a brief 5-10 minute warm–up before entering the "stimulus zone" and a 5-10 minute cool-down after completing the "stimulus zone" work-out. The warm-up is usually a lighter version of the stimulus and is to ensure the body is prepared to be stressed, whereas the cool-down is usually a relaxing set of stretches to enable the body to return to the pre-exercise non-stressed state. Therefore, at least 30 minutes needs to be allotted for the first week of a beginning exercise session (5 minute warm-up, ~20 minute stimulus, 5 minute cool-down), and more time thereafter as one's exercise prescription is

Another aspect of "time" is the actual timing of the exercise – that is, time of day. While this does not impact the dose-response of exercise per se, it does impact the effectiveness of the

upgraded, or progressed through several weeks of a research study.

consequences if a subject veers off course.

**5.1.3 Time ("T"), or duration, of exercise** 

depending upon the nature of the training.


*Source:* Modified from: Nieman, D. *Exercise Testing and Prescription, A Health Related Approach.* 7th Edition, New York: McGraw Hill Publishers, 2011, pp 180, Table 6.3, Classification of Physical Activity Intensity

Table 1. Intensity scales equating verbal descriptions to percent heart rate reserve (%HRR), percent heart rate max (%HRmax), rating of perceived exertion (RPE) based on the Borg 6-20 scale, and percent of a one-repetition maximum (%1-RM) strength test.

A slightly more complex, but more accurate way to prescribe aerobic exercise intensity is by using the Karvonen formula, a mathematical formula using percentage of one's heart rate reserve (maximal heart rate – resting heart rate). This requires knowing one's maximal heart rate (or estimating it as shown above), knowing one's resting heart rate (being able to take one's pulse rate at rest) and using the percentages listed in *Table 1*. Because this calculation more closely represents oxygen consumption requirements, the percentages shown in the table are slightly lower than the ones used with the age-predicted heart rate max method just described. Thus, the formula for determining a moderate-intensity heart rate stimulus zone using the Karvonen Method is as follows:

[(Maximal Heart Rate – Resting Heart Rage) \* 40%] + Resting Heart Rate

[(Maximal Heart Rate – Resting Heart Rage) \* 59%] + Resting Heart Rate

Thus, if our 50-year old person had a resting pulse rate of 75 bpm, using the Karvonen method to determine his exercise stimulus zone, his heart rate training stimulus zone would be 113 to 131 bpm.

#### **5.1.2.2 Perception of effort**

Sometimes heart rate responses are modified by medications or the exercise participant simply cannot take his/her pulse rate. In that case, exercise can be prescribed based on one's perception of the exercise intensity. This is called "rating of perceived exertion", or RPE. The most common RPE scale used is Borg's 6-20 scale, which at moderate intensity exercise, correlates well with the heart rate response. For instance if a person rates his level of exertion to be between 12-14, the heart rate is generally within 120-140 beats per minute. It does take about 3 practice sessions for the user to become familiar and comfortable with this scale in order to get the most accurate RPE scores **(**Borg, 1985). For a more complete understanding of using perceived exertion, an excellent applied book is "*Perceived Exertion for Practioners*" (R.J. Robertson, 2004, Human Kinetics Publishers).

#### **5.1.2.3 Workload**

When utilizing equipment for exercise training, the intensity of training will in part be mediated by the workload setting employed. For instance, if a moderate intensity is desired for lifting weights on a machine, a percentage of what a person is able to lift maximally one time (% 1-RM) maybe used. As seen in *Table 1*, to strength train at a moderate intensity, approximately 40-69% of a 1-RM will be recommended. That means, if the maximum weight one is able to lift is 100 pounds, then the training weight stack should be between 40 and 69 pounds (or, 45 kg max = 18 to 31 kg). If using a treadmill, the exerciser would need

*Source:* Modified from: Nieman, D. *Exercise Testing and Prescription, A Health Related Approach.* 7th Edition, New York: McGraw Hill Publishers, 2011, pp 180, Table 6.3, Classification of Physical Activity

Table 1. Intensity scales equating verbal descriptions to percent heart rate reserve (%HRR), percent heart rate max (%HRmax), rating of perceived exertion (RPE) based on the Borg 6-20

A slightly more complex, but more accurate way to prescribe aerobic exercise intensity is by using the Karvonen formula, a mathematical formula using percentage of one's heart rate reserve (maximal heart rate – resting heart rate). This requires knowing one's maximal heart rate (or estimating it as shown above), knowing one's resting heart rate (being able to take one's pulse rate at rest) and using the percentages listed in *Table 1*. Because this calculation more closely represents oxygen consumption requirements, the percentages shown in the table are slightly lower than the ones used with the age-predicted heart rate max method just described. Thus, the formula for determining a moderate-intensity heart rate stimulus

[(Maximal Heart Rate – Resting Heart Rage) \* 40%] + Resting Heart Rate

[(Maximal Heart Rate – Resting Heart Rage) \* 59%] + Resting Heart Rate

*for Practioners*" (R.J. Robertson, 2004, Human Kinetics Publishers).

Thus, if our 50-year old person had a resting pulse rate of 75 bpm, using the Karvonen method to determine his exercise stimulus zone, his heart rate training stimulus zone would

Sometimes heart rate responses are modified by medications or the exercise participant simply cannot take his/her pulse rate. In that case, exercise can be prescribed based on one's perception of the exercise intensity. This is called "rating of perceived exertion", or RPE. The most common RPE scale used is Borg's 6-20 scale, which at moderate intensity exercise, correlates well with the heart rate response. For instance if a person rates his level of exertion to be between 12-14, the heart rate is generally within 120-140 beats per minute. It does take about 3 practice sessions for the user to become familiar and comfortable with this scale in order to get the most accurate RPE scores **(**Borg, 1985). For a more complete understanding of using perceived exertion, an excellent applied book is "*Perceived Exertion* 

When utilizing equipment for exercise training, the intensity of training will in part be mediated by the workload setting employed. For instance, if a moderate intensity is desired for lifting weights on a machine, a percentage of what a person is able to lift maximally one time (% 1-RM) maybe used. As seen in *Table 1*, to strength train at a moderate intensity, approximately 40-69% of a 1-RM will be recommended. That means, if the maximum weight one is able to lift is 100 pounds, then the training weight stack should be between 40 and 69 pounds (or, 45 kg max = 18 to 31 kg). If using a treadmill, the exerciser would need

scale, and percent of a one-repetition maximum (%1-RM) strength test.

zone using the Karvonen Method is as follows:

Intensity %HRR %Max HR (bpm) RPE Range % 1-RM Moderate 40-59 64-76 12-14 40-69 Hard /Vigorous 60-84 77-93 14-15 50-69

Intensity

be 113 to 131 bpm.

**5.1.2.3 Workload** 

**5.1.2.2 Perception of effort** 

instructions as to how to set the speed and percent grade; if using a cycle ergometer, the exerciser would need to know how to set the resistance and at what speed to pedal. Sometimes this is determined by an entry exercise test and the settings are based upon a percentage of their max test results; other times it is arbitrarily determined and governed simply by determining a "comfortable" pace in order to attain a desired heart rate or RPE range. Using the latter method will enable the researcher to permit the exerciser to exercise on a greater variety of equipment, thereby helping to reduce exercise boredom and dropping out of a study. However, a word of caution: if the goal of the research is to determine the impact of a certain TYPE of exercise on the brain over a certain period of time, then the researcher must give explicit instructions as to which equipment use is permissible for exercise research participation. Sometimes, giving a research volunteer too many choices can truly confound interpretation of the research results. Thus, while that new exercise club down the road may be convenient and affordable for the study, the researcher must determine how precisely the exercise prescription must be adhered to and consider the consequences if a subject veers off course.

#### **5.1.3 Time ("T"), or duration, of exercise**

The first "T" of the FITT + P paradigm is Time. How "long" one exercises, or how much time is required to achieve a desired fitness benefit, depends upon one's health status and/or fitness goals, and as stated above, the frequency of exercise. If one is very deconditioned, then multiple sessions of brief duration may be recommended. These brief durations may be as little as 5 minutes. It is common for those with a fragile health status or simply deconditioned due to inactivity (but otherwise considered healthy) to be given an intermittent exercise prescription consisting of 5 minutes of physical activity interspersed with an equal amount of rest, with that dose repeated twice more in succession so that an equivalent of 15 minutes can be accrued. As one successfully adapts to the exercise stimulus, the rest sessions will be reduced so that eventually the previously deconditioned person can exercise for 15 continuous minutes. Once a baseline level of aerobic endurance is attained, then strength conditioning can be safely and effectively added to the exercise program. As indicated above, an exercise session focusing only on aerobic conditioning can require 15 to 30+ minutes. A strength conditioning program may also require 30+ minutes if the entire body is to be trained in one session. Flexibility training can be a stand-alone program or be incorporated into the regular exercise program as part of a warm-up and/or cool-down routine. Thus, flexibility training can take as little as 5 minutes or as long as 30 minutes, depending upon the nature of the training.

While any one component of an exercise program may eventually take about 30+ minutes, it is standard to also incorporate a brief 5-10 minute warm–up before entering the "stimulus zone" and a 5-10 minute cool-down after completing the "stimulus zone" work-out. The warm-up is usually a lighter version of the stimulus and is to ensure the body is prepared to be stressed, whereas the cool-down is usually a relaxing set of stretches to enable the body to return to the pre-exercise non-stressed state. Therefore, at least 30 minutes needs to be allotted for the first week of a beginning exercise session (5 minute warm-up, ~20 minute stimulus, 5 minute cool-down), and more time thereafter as one's exercise prescription is upgraded, or progressed through several weeks of a research study.

Another aspect of "time" is the actual timing of the exercise – that is, time of day. While this does not impact the dose-response of exercise per se, it does impact the effectiveness of the

MRI Techniques to Evaluate Exercise Impact on the Aging Human Brain 237

the physiological systems so that the body can continually respond and successfully adapt to the overload. Unsuccessful adaption to an overload will result in undue fatigue,

Perhaps the most important concept to understand is the complex interaction between intensity, frequency and duration of the exercise prescription and how manipulation of any one of these variable impacts the exercise progression and adaption. The way to avoid unsuccessful overloading is to increase only one exercise prescription component in any given exercise session. For example, if the frequency of exercise training is scheduled to be increased from 3 days a week to 4 days a week, then the duration (total time) and intensity of the exercise session should remain the same as the previous training session. If on the other hand, the intensity of exercise needs to be increased, then the duration of the exercise session should either remain the same or be decreased slightly to accommodate for the increased effort required. On the following day, the duration can be returned to its previous level as long as the "new" exercise intensity remains the same. *Figure 1* outlines the basic components of the exercise prescription and can serve as a quick-reference exercise dosing

• Type:

**F:** 2-3 days/wk; **I:** 8-15 reps; 8-10 exercises; 1-3 sets 50-80% 1RM **T:** 30 - 60 min.

**P:** Every 1 to 2 weeks: 2 to 15% Increase or 2 to 10 min increase Muscular Conditioning

Fig. 1. Exercise prescription components featuring the FITT + P paradigm. Less active, unfit individuals would have exercise dosing at the lower ranges where as more active, higher fit individuals would have exercise dosing at the higher ranges. HR = heart rate; RPE = rating

• Type: • Progression

of perceived exertion.

Flexibility

• Type:

Aerobic Endurance

unnecessary muscle soreness, and if extreme, illness and/or injury.

**F:** 3-5 d/wk; **I:** Moderate to vigorous HR or RPE Speed, % grade, steps or rows/min.

**T:** 15-60 min.

**F:** 2-3 d/wk **I:** 5-30 sec holds **T:** 5 - 20 min.

~ 8 exercises utilizing both upper and lower body

exercise plan if the time of day allotted to exercise is not compatible with the exerciser's lifestyle. For instance, if exercise is to take place under supervised conditions at a facility, the hours must be agreeable with the exercise's life – are there times available before or after one's work day, or at lunch? If recruiting a person with child care responsibilities, are there childcare services? Are weekend hours available? Other concerns are parking, commuting time, or easy bus/rail access. Will the research study pay for on-site childcare or parking?

#### **5.1.4 TYPE ("T") of exercise**

The other "T" component of the FITT + P paradigm is the TYPE of exercise (or activity) needed to achieve the stated research goals. The exercise prescription type is subdivided into three broad categories: aerobic endurance (or fitness), muscular strength/endurance, and flexibility. Of course each of these broad activity categories has numerous subtypes, thus it is crucial to specifically describe the type of activity one is to engage in. For instance, an aerobic activity is any activity that a person can complete continuously for 15 minutes or more that utilizes a large portion of the body's musculature in a rhythmic fashion. This includes common individual activities such as walking, running, swimming and cycling but it can also include games, sports and various types of dance. Muscular strength/endurance training also has many sub-types. It can consist of the traditional lifting of weights (aka weight training) or it can be termed resistance training or core training and involve not only dumbbells, free weights, or machines, but also medicine balls, resistance bands and tubing, kettle balls and one's own weight (e.g. push-ups, sit-ups). Other types of musculoskeletal training can include balance training, plyometric training, neuromuscular facilitation training, yoga, and tai chi. Flexibility training can involve static, ballistic, or dynamic stretching. Often times, strength and conditioning programs are simply called "stretching and toning", which really provides no concrete idea of the type of training actually provided. Thus, with all these options available to the researcher, creating a reproducible exercise program to investigate a particular health parameter becomes an art form. Obviously it is not possible to investigate every aspect of exercise within one study, so the researcher must narrow his/her focus to a select few options and describe them wellenough for the reader to be able to replicate. Ultimately, with enough well-designed neurobiology exercise studies, general recommendations for cerebral health will be able to be created, similar to those that now exist for cardiovascular health.

#### **5.1.5 Progression ("P") of exercise**

There are a variety of ways to "progress" an exercise prescription so that it remains challenging yet doable for the participant and prevents boredom or staleness. The progression of exercise is increased over the ensuing weeks at a percentage that is both safe and effective for that particular individual. The eventual goal is for one to attain a minimum of 30 or more minutes of continuous exercise on most days of the week (Haskell et al., 2007). One rule of thumb has been to increase any given exercise dose by as little as 2% or as much as 30% weekly or every other week. Another practice is to increase the duration of exercise by approximately 5 to 10 minutes every week, which might translate to a 15% increase in time week to week. If there is little room for adding additional time to an exercise session, then an extra day of training can be added on. If neither time nor frequency is an option to increase, then intensity becomes the progression target. When a person's perception of effort decreases along with lower heart rate responses with any given exercise stimulus, it is time to increase the exercise intensity. The goal is to make sure a slight overload is placed upon

exercise plan if the time of day allotted to exercise is not compatible with the exerciser's lifestyle. For instance, if exercise is to take place under supervised conditions at a facility, the hours must be agreeable with the exercise's life – are there times available before or after one's work day, or at lunch? If recruiting a person with child care responsibilities, are there childcare services? Are weekend hours available? Other concerns are parking, commuting time, or easy bus/rail access. Will the research study pay for on-site childcare or parking?

The other "T" component of the FITT + P paradigm is the TYPE of exercise (or activity) needed to achieve the stated research goals. The exercise prescription type is subdivided into three broad categories: aerobic endurance (or fitness), muscular strength/endurance, and flexibility. Of course each of these broad activity categories has numerous subtypes, thus it is crucial to specifically describe the type of activity one is to engage in. For instance, an aerobic activity is any activity that a person can complete continuously for 15 minutes or more that utilizes a large portion of the body's musculature in a rhythmic fashion. This includes common individual activities such as walking, running, swimming and cycling but it can also include games, sports and various types of dance. Muscular strength/endurance training also has many sub-types. It can consist of the traditional lifting of weights (aka weight training) or it can be termed resistance training or core training and involve not only dumbbells, free weights, or machines, but also medicine balls, resistance bands and tubing, kettle balls and one's own weight (e.g. push-ups, sit-ups). Other types of musculoskeletal training can include balance training, plyometric training, neuromuscular facilitation training, yoga, and tai chi. Flexibility training can involve static, ballistic, or dynamic stretching. Often times, strength and conditioning programs are simply called "stretching and toning", which really provides no concrete idea of the type of training actually provided. Thus, with all these options available to the researcher, creating a reproducible exercise program to investigate a particular health parameter becomes an art form. Obviously it is not possible to investigate every aspect of exercise within one study, so the researcher must narrow his/her focus to a select few options and describe them wellenough for the reader to be able to replicate. Ultimately, with enough well-designed neurobiology exercise studies, general recommendations for cerebral health will be able to

be created, similar to those that now exist for cardiovascular health.

There are a variety of ways to "progress" an exercise prescription so that it remains challenging yet doable for the participant and prevents boredom or staleness. The progression of exercise is increased over the ensuing weeks at a percentage that is both safe and effective for that particular individual. The eventual goal is for one to attain a minimum of 30 or more minutes of continuous exercise on most days of the week (Haskell et al., 2007). One rule of thumb has been to increase any given exercise dose by as little as 2% or as much as 30% weekly or every other week. Another practice is to increase the duration of exercise by approximately 5 to 10 minutes every week, which might translate to a 15% increase in time week to week. If there is little room for adding additional time to an exercise session, then an extra day of training can be added on. If neither time nor frequency is an option to increase, then intensity becomes the progression target. When a person's perception of effort decreases along with lower heart rate responses with any given exercise stimulus, it is time to increase the exercise intensity. The goal is to make sure a slight overload is placed upon

**5.1.5 Progression ("P") of exercise** 

**5.1.4 TYPE ("T") of exercise** 

the physiological systems so that the body can continually respond and successfully adapt to the overload. Unsuccessful adaption to an overload will result in undue fatigue, unnecessary muscle soreness, and if extreme, illness and/or injury.

Perhaps the most important concept to understand is the complex interaction between intensity, frequency and duration of the exercise prescription and how manipulation of any one of these variable impacts the exercise progression and adaption. The way to avoid unsuccessful overloading is to increase only one exercise prescription component in any given exercise session. For example, if the frequency of exercise training is scheduled to be increased from 3 days a week to 4 days a week, then the duration (total time) and intensity of the exercise session should remain the same as the previous training session. If on the other hand, the intensity of exercise needs to be increased, then the duration of the exercise session should either remain the same or be decreased slightly to accommodate for the increased effort required. On the following day, the duration can be returned to its previous level as long as the "new" exercise intensity remains the same. *Figure 1* outlines the basic components of the exercise prescription and can serve as a quick-reference exercise dosing

Fig. 1. Exercise prescription components featuring the FITT + P paradigm. Less active, unfit individuals would have exercise dosing at the lower ranges where as more active, higher fit individuals would have exercise dosing at the higher ranges. HR = heart rate; RPE = rating of perceived exertion.

MRI Techniques to Evaluate Exercise Impact on the Aging Human Brain 239

for an hour each session not only prevented brain volume atrophy but resulted in brain volume improvement in older adults (Colcombe et al., 2006). Using voxel-based morphology, improvements in brain volume were noted in both the gray and white matter regions associated with executive function, long term memory, and general intelligence (i.e., the prefrontal and temporal cortices). These improvements were cautiously reported in terms of brain atrophy risk reduction in comparison to a stretching/toning control group such that a 16% improvement in aerobic fitness resulted in a 27 to 42% risk reduction of brain atrophy. The greatest risk reduction was in the anterior cingulate cortex. The stretching/toning group experienced a non-significant 5% increase in aerobic fitness but no volumetric information was reported for them. Although it is not known if the 5% improvement in aerobic fitness also resulted in some volumetric improvement, it might be surmised that embarking upon a moderate-intensity aerobic exercise program which produces at least a 1% increase in aerobic fitness may attenuate aging-related brain atrophy. This was one of the first longitudinal outcome studies reporting the impact of aerobic versus

Currently, little neuroimaging information is available on other modes or durations of exercise training; nor is there information regarding how quickly the human brain structure detrains. But if the brain/cerebrovasculature mirrors the heart/cardiovasculature in exercise adaptations, then like the cardiovascular system, the cerebrovascular system may lose that 11% gain in as little as 3 weeks of no training (Coyle et al., 1984). Thus, the protective effect against brain atrophy may be lost in one short month if one is unable to exercise sufficiently. An intriguing question remains, can cognitive brain training (e.g. suduko, puzzles, playing chess, Wii-games) supplant physical activity during periods of

Being a pioneer in exercise and aging neuroscience research also means there will likely be design flaws in the research. For instance, in Colcombe et al's study (2006), the age range was wide, 60 to 79 years with a mean age of 66 years. The study age range spanned two decades with three standard aging cohorts: the older end of middle-aged (45-64 years old), the young-old (65-74 years old), and the younger end of old (75-84 years old). No mention was made regarding how many subjects fell within each of these age cohorts, therefore it is not known if these age cohorts responded differently to the exercise programs. With no variance measure or age range provided *per group* on any variable, it is difficult to assume the study did not have a few inadvertent biases. A potential younger-age bias may have preexisted in the aerobic treatment group (the treatment group was on average 1.4 years younger). The stretching/toning control group had a slightly higher percentage of females (4% more), creating a potential gender bias. Further, the actual pre-aerobic fitness distribution per grouping was unclear. Although the mean aerobic fitness (VO2) values were not significantly different between groups (~ 23 ml/kg/min), the pre-intervention VO2 values ranged from 12.9 to 49.9 ml/kg/min. Thus there were some older individuals with pre-intervention VO2 values who would be considered highly fit and therefore have less room for improvement from any type of intervention. It is not known if an attempt was made to balance the placement of these higher-fit individuals into the two groups since the methods claim group assignment was totally randomized. Furthermore, it was reported that the aerobic group was previously sedentary, however older adults with VO2's exceeding 40 ml/kg/min are not likely habitually sedentary. Individually, the between group differences highlighted here are small and were

musculoskeletal-type exercise on the aging brain.

**6.3 Exercise neuroimaging study shortcomings** 

physical inactivity in order to maintain brain structure and function?

guide. More complete exercise prescription information is available in the ACSM's Guidelines for Exercise Testing and Prescription book (2009), updated every four years. The best advice for researchers using exercise as a research treatment arm, or clinicians using exercise as a therapeutic agent is to make sure one or more ACSM-certified exercise physiologists are a part of your team.
