Effects of acute aerobic exercise on executive function in older women.

Author:Peiffer, Roseann
Position:Research article
 
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Introduction

There is a high prevalence of decreased cognition in the aging population (Chan et al., 2005). One of the typical characteristics of non-pathological brain aging includes some loss of cognitive function (Erickson and Kramer, 2009). Executive functions (reaction time and attention tasks) are a part of cognitive function and include tasks demanding diligence, conscious control, and the processing of new information. These executive functions typically involve the frontal, prefrontal, and parietal portions of the brain (Colcombe et al., 2004). Structural, physiological, and psychological changes in the frontal part of the brain are common in older adults (Colcombe et al., 2004).

There has been increasing evidence that regular physical activity can help prevent, or at least delay, the onset of cognitive loss (Colcombe and Kramer, 2003). Erickson and Kramer (2009), and Hillman, Snook, and Jerome (2003) have reported that cognitive function is the brain function most positively affected by cardiovascular exercise. Participation in aerobic exercise and physical activity seems to have a strong shielding effect on brain function and anatomy in many older adults as well as those who are susceptible to the development of cognitive deterioration (Churchill et al., 2002; Colcombe and Kramer, 2003). Cardiovascular exercise appears to considerably reduce the loss of brain tissue in regions controlling executive function (Colcombe and Kramer, 2003). Executive function describes attention, reaction time, and response accuracy. Executive function manipulates, controls, and organizes other aspects of cognition, and includes a wide variety of tasks, such as planning, attention, problem-solving, the initiation and directing of actions, task-switching, reasoning, and multitasking (Beilock and Carr, 2005). In older adult brains, improvements in baseline aerobic fitness can supply an amount of plasticity and resilience to neural substrates that is absent in the elderly who possess a low fitness status (Colcombe et al., 2004). It is believed that participation in exercise that improves aerobic capacity helps increase oxygen-rich blood flow to the brain, which facilitates normal physiological processes (Colcombe et al., 2004).

Implications have been made that acute aerobic exercise helps increase cognitive processing speed among tasks demanding a substantial degree of executive function (Hillman et al., 2003; Kamijo et al., 2007). Kamijo et al. (2009) reported that older adults 60-74 years of age, had elements of executive function such as reaction time, and response accuracy improved after an acute bout of "moderate" (50% of [VO.sub.2]max), but not "light" (30% of [VO.sub.2]max) aerobic exercise. While Kamijo et al. (2009) noted that executive function was improved after moderate exercise; it is unclear how cognition will be improved in older adults after higher intensity exercise [i.e., >60% of [VO.sub.2]max; 60-84 %[VO.sub.2]max--defined as "vigorous" (ACSM, 2014)], especially if they are not chronic aerobic exercisers (Pesce, 2009).

The effect of high intensity exercise on executive function has been investigated by Kamijo et al. (2004) and Budde et al. (2012) in young adults. Kamijo et al. (2004) found that executive function decreased after an acute about of high-intensity aerobic exercise (i.e., maximal cycling GXT) in young adult males. Conversely, Budde et al. (2012) reported that in young adults, only those who exercised regularly displayed improvements in executive function after high-intensity aerobic exercise (i.e., 20-m sprints for 3 min to max HR two times). In addition, Hogervorst, Riedel, Jeukendrup, and Jolles (1996) and Winter et al. (2007) reported that cognition could be increased after high-intensity exercise bouts of 75% of maximal work rate. Therefore, cognition does not always decline after high-intensity exercise, such as sprinting in young adults (Winter et al., 2007).

Because many of the studies on cognitive responses to acute exercise have been performed on younger adults, the purposes of this study were to investigate in older women who were aerobically fit: 1) whether cognitive function (i.e., reaction times from the flanker test, and results from a d2 test) changed after acute bouts of moderate or vigorous exercise; 2) if changes in cognitive function existed 30 minutes after exercise at each intensity; 3) whether the aerobic fitness of older women ([greater than or equal to] 60 years of age) was related to cognitive function after acute bouts of moderate and high-intensity exercise.

Methods

Design

The study design was a pre-test/post-test experimental study with the treatment (exercise trials at a moderate or at a vigorous intensity; Pre-Ex) performed after baseline fitness testing of the participants. After each exercise trial performed to the participant's target HR, the dependent variables were measured immediately after exercise (Imm-Ex) and at 30 minutes after exercise (Post-30). Dependent variables for the study were Total Reaction Time ([RT.sub.T]), Incongruent Reaction Time ([RT.sub.I]), Congruent Reaction Time ([RT.sub.C]), Error rate (i.e., the relative number of all errors of confusion and elimination), GZ value (i.e., the rate at which participants mark off each d2 and the overall number of marked letters within the d2 test), and SKL value (i.e., a measure of attention; the standardized number of accurate answers minus confusion errors).

Participants

Women, 60-75 years of age (n = 11), were recruited from a midwestern university and surrounding community. Only women were chosen because few studies have been conducted investigating exercise and cognition of older women. Females may be at a greater risk for developing cognitive decline because of the decrease in estrogen levels at menopause (Spirduso et al., 2008). Any participant who was taking medications for cognitive impairment was excluded, as well as individuals who were on blood pressure medications, antidepressants, or medications for mental illness. There were 10 women who were screened out of the study because of medications; about 50% of the respondents participated in the study. A physician's consent form was obtained by each participant before involvement in the study. Participants gave their informed consent, and this study was approved by the Human Subjects Review Board at the university.

Measures

Baseline Physiological and Fitness Tests

Determination of predicted [VO.sub.2]max: A measure of each participant's fitness level was assessed by having each participant complete a submaximal graded exercise test (GXT) (Balke Protocol) walking on a motorized treadmill. A submaximal graded exercise test was given instead of a maximal graded exercise test because submaximal tests of cardiovascular fitness do not require a physician's presence, provide lower risks than exercising at maximal intensity, and are fairly precise in predicting [VO.sub.2]max (ACSM, 2014). Participants walked on the treadmill until their heart rate reached 85% of their age-predicted maximal HR calculated from 206.9--(.67*age) (ACSM, 2014). The protocol included a 3-minute warm-up period at 2.0 mph before the first stage (ACSM, 2014). Blood pressure via auscultation, and heart rate via electrocardiograph (EKG) were measured before the test, as well as during each stage of the GXT (ACSM, 2014). Ratings of perceived exertion (RPE) using the 15-point (6-20) Borg (1973) scale were recorded at the end of each stage of the GXT.

Waist and hip circumferences: Waist and hip circumferences (cm) were used to determine distribution of body fat and health risk. A Gulick tape was used to measure these circumferences according to standard procedures (ACSM, 2014). The waist-to-hip ratio (WHR) was calculated from these values.

International Physical Activity Questionnaire (IPAQ) (Hagstromer et al., 2006): The IPAQ is a popular and valid physical activity questionnaire used internationally to assess physical activity levels (Hagstromer et al., 2005). The IPAQ has three ratings. A 3 designates those who are highly active and participate in 30 minutes of high-intensity exercise, or an hour or more of moderate-intensity exercise above the basal level of physical activity (approximately 5,000 steps per day) (iPAQ, 2005). Individuals who are highly active are also classified by completing 12,500 or more steps per day (IPAQ, 2005). Those who are rated at a moderate physical activity score of a 2 are active for 30 minutes on most days of the week at a moderate-intensity (IPAQ, 2005). Individuals who score a 1 are considered low active and do not meet any of the criteria for moderate or high active (IPAQ, 2005). The IPAQ also classifies individuals into a low, moderate, or high category as a sum of MET-minutes/week (IPAQ, 2005). Those who are high active, or category 3, score at least 3000 MET-minutes/week from total physical activity levels (walking, moderate, or high-intensity exercise), or 1500 MET-minutes/week from high-intensity exercise (IPAQ, 2005). Individuals who are categorized as a 2, or are moderately active, attain at least 600 MET-minutes/week (IPAQ, 2005). Those who are categorized as a 1, or are low active, do not meet the criteria for categories 2 or 3 (IPAQ, 2005).

Executive Function Tests - Modified flanker task and d2 test (Budde et al., 2012; Kamijo et al., 2009): The modified flanker task measures reaction time and response accuracy, which are aspects of inhibitory control and executive function (Kamijo et al., 2007; Kamijo et al., 2009). The test was administered on a computer screen, where 5 arrows were shown per situation. There were 80 situations, 40 congruent and 40 incongruent. In the congruent situation, arrows are displayed that point in the same direction as the middle arrow, the arrow of reference, allowing quicker reaction time (e.g., [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]). In the incongruent condition, the arrow...

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