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_T), Incongruent Reaction Time (RT_I), Congruent Reaction Time (RT_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).

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.

Each participant reported to the exercise physiology laboratory three times at the same time of day, 4-7 days apart. When arriving for the first visit (i.e., baseline fitness testing), each participant was given an informed consent form, a medical history questionnaire, and the long version of the International Physical Activity Questionnaire (IPAQ) (Hagströmer et al., 2006). After completing all of these forms, participants had their height and body mass measured, and body mass index (BMI) was calculated. Waist and hip circumferences (cm) were measured with a Gulick tape and WHR was calculated (ACSM, 2014). Demographic data are shown in Table 1.

For the baseline fitness testing and the exercise trials, the modified flanker task and d2 test were given before exercise to assess executive function. In order to reduce the effects of learning (Davranche et al., 2009; Kamjio et al., 2009), 32 practice trials of the modified flanker task and 3 lines of the d2 test were permitted before the protocol for the VO₂max test and exercise trials. After practice, either 80 real trials (40 congruent and 40 incongruent situations) of the modified flanker test and the d2 test were completed first with the order of the tests alternated.

After these cognitive tasks were completed prior to (Pre-Ex) the baseline fitness testing or exercise trials, the GXT or exercise trials were completed. Less than two minutes after exercise (Imm-Ex), participants again completed 80 trials of the modified flanker task (Kamjio et al., 2009) followed by 14 lines of the d2 test. The modified flanker task and d2 test were taken again 30 minutes post-exercise (Post-30). During the waiting period, participants were given magazines to read, as well as water. For the d2 test of selective and sustained attention, each dependent variable of the d2 test was normalized into a ratio because the total number of d2’s in each test was not the same. The number of d2’s in each test was randomized because if the total number of d2’s were identical in each test, participants might start to recognize a pattern.

During the exercise trials, the participants were alternately assigned to a moderate exercise session at 50% of their estimated VO₂max for 20 minutes, following a 5-minute warm-up period of walking, or a vigorous intensity exercise session at 75% of their estimated VO₂max for the same duration. The duration of 20 minutes was chosen because previous studies with exercise of 15 to 20 minutes had an impact on cognitive functioning (Davranche et al., 2005, 2006; Davranche and Audiffren, 2004; Kamijo et al., 2009). Budde et al. (2010) noted previously that exercise intensity is more important than exercise duration when investigating the endocrine response and cognition. In this study, cognition was measured before and after moderate and high intensity aerobic exercise of the same duration. The exercise intensity at a percentage of VO₂max was estimated using metabolic equations (ACSM, 2014). The speed was set at 3.0 mph while the grade was manipulated by the researcher to ensure each participant reached the specified intensity after the warm-up period. Each participant completed both intensities of exercise on separate days. HR, blood pressure, and RPE were recorded every 5 minutes during each 20-min exercise session (Kamjio et al., 2009). The modified flanker and d-2 tests were administered similarly to the baseline fitness testing session.

Means and standard deviations were calculated for all variables. Appropriate two-way repeated measures (2 w 3; Exercise Intensity c Time) ANOVAs were used to determine if there were significant differences between means for the various levels of the independent variables. Level of significance was set at p 0.05. Appropriate post hoc tests were calculated to determine where the differences occurred, if applicable. Pearson correlations for VO₂max with each dependent variable at each time, and for VO₂max with the difference scores for Pre-Ex to Imm-Ex were calculated.

Demographic data for the participants are shown in Table 1. The mean BMI for the women was 24.2 and was in the “normal” range (ACSM, 2014), and the mean WHR of 0.75 was in the “low” risk category (ACSM, 2014). The mean estimated VO₂max value for participants was 36.8 ml·kg^-1·min^-1; for this age group this is rated as superior (ACSM, 2014). Results from the IPAQ indicated that 7 women were highly active, while 4 were moderately active. The average Total IPAQ Physical Activity Score for participants was 6857 MET-minutes, while their mean IPAQ rating was 2.6. Those who had the highest VO₂max values in this study scored a 3 for high physical activity levels, while those who scored a 2 for moderate physical activity levels had lower VO₂max values. This indicates the participants from this study were moderate to highly active, generally of low risk for cardiovascular disease, and not on any medications.

Correlations were calculated between VO₂max and the dependent variables at Pre-Ex, Imm-Ex, or Post-30 by exercise intensity and are shown in Table 4. VO₂max was correlated with three of the dependent variables, RT_T Pre-Ex and RT_T Post-30 for both intensities, RT_T at all time periods except RT_I Imm-Ex vigorous intensity, and for RT_C for moderate Intensity exercise at Pre-Ex and Post-30 but not for vigorous intensity exercise (see Table 4). Only two correlations of VO₂max with change scores (i.e., Pre-Ex minus Imm-Ex values) for RT_T Moderate Intensity, r = 0.619, p = 0.028 and RT_C Moderate Intensity, r = .619, p = 0.028 were significant. No other correlations were significant.

Reaction time results from the modified flanker task (i.e., RT_T, RT_I, and RT_C) improved after acute exercise (i.e., Imm-Ex) regardless of exercise intensity (i.e., moderate intensity and vigorous intensity). RT_T and RT_C did not stay improved after 30 min of recovery. However, the effects of acute exercise remained for RT_I as improve-ment was sustained after 30 minutes of recovery (see Figure 2). These results are comparable to the findings by Kamijo et al. (2009), who reported that reaction time was improved immediately after moderate-intensity (i.e., 50% VO₂max) exercise for older males (60-74 years) and younger males (19-25 years). They had participants complete a modified flanker task before and less than 2 minutes after both a light (30% VO₂max) and moderate (50% VO₂max) 20-min cycling session. After exercising at 50% VO₂max, reaction time significantly decreased for both age groups. However, the exercise session at 30% VO₂max resulted in no significant decrease in reaction time as compared to baseline. Davranche et al. (2009) also used a modified version of the Eriksen flanker task, which measures executive function, and found that during 20 minutes of cycling at a moderate intensity of 50% of maximal aerobic power, congruent and incongruent reaction times were improved in university students and staff compared to baseline. Immediately after aerobic exercise at both moderate and vigorous intensities (50% VO₂max and 75% VO₂max) in this study, older adult females (60-75 years) significantly decreased their reaction times (i.e., RT_T, RT_I, and RT_C) as well. Therefore, reaction time improved regardless of the intensity of exercise.

In this study, the changes in incongruent RT were greater than in the congruent condition. This may be because incongruent RT uses a larger portion of executive function processing (Hillman et al., 2003; Kamijo et al., 2007) than the congruent condition. The incongruent arrows cause a slower reaction time due to the stimulation of an inaccurate answer before the task is finished (Hillman et al., 2003). This is because the surrounding arrows point in opposite directions as compared to the middle arrow, the arrow that participants are expected to react to (Kamijo et al., 2009). The accurate answer brought out by the target stimulus is challenged in the incongruent condition (Hillman et al., 2003; Kamijo et al., 2009). Older adult females had faster reaction times in incongruent condition immediately after exercise, as well as 30 minutes after exercise for both exercise intensities. In contrast, for the congruent condition, reaction time was only significantly improved from immediately after exercise. It appears that the incongruent condition elicited greater reaction time changes. The incongruent condition of a flanker task requires a larger extent of executive function than the congruent condition (Colcombe et al., 2004).

The findings from this study of the reaction time effect for the incongruent condition also are important because acute aerobic exercise of moderate and vigorous intensities can improve executive function processes in older women who possess a high level of fitness (i.e., mean VO₂max was 36.8 ml·kg^-1·min^-1 in this study). The VO₂max of the participants was considered superior for females 60-79 years of age (ACSM, 2014), and was between the 90-95 percentiles. This supports the results of Colcombe et al. (2004) who assessed fitness levels of older adults using the Rockport 1-mile walk test. They reported that older adults with higher fitness levels displayed a greater reduction in reaction time during the incongruent condition of a flanker task as compared to those with lower fitness levels. Because of a small sample size, participants in the present study could not be stratified by fitness level, and served as their own controls. Future studies may include a control group and fitness stratification of older women not taking medications to further delineate whether aerobic fitness levels effects on RT changes after acute exercise in aerobically fit older adults are comparable to their less fit counterparts.

In older adults, executive function may be responsible for controlling how they walk, particularly during more difficult predicaments such as walking up stairs or walking outside in icy conditions (Mirelman et al., 2012). Because of this, the risk of a fall may increase due to declining executive functioning (i.e., reaction time and attention). At rest, participants in this study of high and moderate fitness possessed similar reaction time scores, however, those who had a higher fitness level displayed a greater reduction in the incongruent condition of a flanker task, which requires a larger extent of executive function than the congruent condition (Colcombe et al., 2004). If executive function can be improved through increases in aerobic fitness, then this knowledge may help motivate some older adults to participate in regular aerobic exercise.

Each d2 test variable that was measured (i.e., error rate, GZ score, and SKL score) improved after exercise, and all were significantly different from baseline at 30 minutes after the completion of exercise, regardless of exercise intensity. The number of total errors (both errors of elimination and confusion), as well as measures of precision and thoroughness, significantly decreased from Pre-Ex to Post-30. This means that aerobic exercise reduces error through 30-minutes post-exercise. The GZ value is the overall number of marked letters (“d” or “p”), whether the marked letter is right or wrong, within the d2 test (Budde et al., 2012). This value corresponds to working speed (how fast one responds in marking off a letter), and significantly increased from Pre-Ex to Imm-Ex, as well as from Pre-Ex to Post-30, meaning that working speed increased after exercise, and persisted 30-minutes post-exercise. The SKL value measures attention span, and is the standardized number of accurate answers minus confusion errors. The SKL value significantly improved from Pre-Ex to Post-30, and from Imm-Ex to Post-30. This means that almost all marked letters were accurately marked as d2’s, therefore, attention span increased across time (Budde et al., 2012). Together, the d2 test variables of Error Rate, GZ, and SKL measure selective and sustained attention, aspects of executive function (Budde et al., 2012) and were improved after acute exercise for these older women.

Stroth et al. (2009) believed that the d2 test of attention requires less concentration, can become automatic, and may not be a reliable task to use in assessing the effects of exercise on attention. In this study participants practiced the d2 test during their baseline session, where fitness status was assessed. They first had a chance to practice 3 lines of the d2 test, and then real trials (14 lines) were taken before their submaximal exercise test. Immediately and 30 minutes after the exercise test, real trials (14 lines) were taken of the d2 test. When participants arrived for their second and third sessions to assess the effects of acute aerobic exercise of moderate and high-intensity on executive function (i.e., attention and reaction time), they had a chance to practice 3 lines of the d2 test, and then took the real trials, 14 lines of the test Pre-Ex, Imm-Ex, and Post-30. Even though the participants had many chances to practice, the results were still improved for the d2 test of attention following aerobic exercise of moderate and high-intensity. It is unlikely participants’ scores changed due to a practice effect, because the number of d2’s in each test was randomized.

Recent evidence proposes that increases in aerobic fitness through regular physical activity are essential to sustain cognition (Hötting and Röder, 2013). In this study, reaction time was significantly lower following both a moderate and high-intensity exercise session for older adult females 60-75 years of age who possessed a superior VO₂max for their age group. This supports results from previous studies. Barnes et al. (2003) reported that higher fitness levels of older adults (68.7 yrs) resulted in improved cognition in their investigation in which they compared high (maxVO₂ = 22.8 to 36.1 ml·kg^-1·min^-1) and low fit (maxVO₂ = 12.3 to 18.6 ml·kg^-1·min^-1) women. Colcombe et al. (2004) also reported that individuals with a higher level of fitness show greater improvements in attention and reaction time after exercise. In addition, Albert et al. (1995) suggested that in adults 70-79 years of age, those who regularly incorporated high-intensity exercise showed less of a decline in cognition. Budde et al. (2012) also studied active and inactive young adults (19-29 years of age) and had them complete the d2 test of attention after intermittent maximal exercise session and a seated control session. Those who were more active were able to improve their attention on the d2 test after the exercise condition, while those who were inactive did not benefit from the exercise session. This finding is similar to results in this study, because older adult females 60-75 years of age who possessed a higher level of aerobic fitness and physical activity participation were able to improve their attention on the d2 test following an acute bout of moderate and high-intensity aerobic exercise. In addition, in the present study, maximal oxygen consumption was not correlated with cognitive variables. However, because of the small sample size these results should be interpreted carefully. There was difficulty in recruiting older females not on medications (a selected criterion for the study), and therefore a comparison between older females with high and low fitness levels was not completed.

Since older adults of a high fitness level participated in this study, this could have significant implications because if older adult women could exercise before they start their day, they might be better able to pay attention to surrounding stimuli, such as during driving. However, according to Kamijo et al. (2007), individuals should first increase their fitness level to gain cognitive benefits. It is believed that decreased blood flow to the frontal lobe in the brain is due to a reduced ability to maintain attention during challenging endeavors in older adults (Mahoney et al. 2010). Because the act of driving a car, planning out business meetings, or balancing a checkbook requires executive function, if a decline in this type of cognition occurs in older adults, they are going to have a more difficult time carrying out these tasks. Since aerobic exercise is known to increase blood flow to the brain (Colcombe et al., 2004), it is important that older adults increase the amount of time they spend participating in aerobic exercise to enhance their fitness so that they can maintain good levels of executive functioning.

Dependent variables were measured immediately after exercise and post-30-minutes to determine the time course for improvement in cognition, if present. Pontifex et al. (2009) tested 21 younger adults (Means: 20.2 years, VO₂max = 54.6 ml^.kg^-1.min^-1) to determine whether acute aerobic exercise, resistance exercise, or both affected cognition after exercise. Participants completed a modified Sternberg task (Sternberg, 1996) that assessed reaction time and response accuracy (i.e., executive function) by displaying a series of letter sequences involving uppercase consonants or lowercase consonants. Participants had to press a key with their right or left thumbs, depending on which sequence was present. Participants completed the Sternberg task before, immediately after, and 30-minutes following 30 minutes of aerobic exercise on a treadmill at 60-70% of VO₂max, 30 minutes of strength training, or a rest condition of 30 minutes. Reaction time decreased immediately after exercise and 30-minutes post-exercise for the aerobic exercise condition only (Pontifex et al., 2009). Hogervorst et al. (1996) found that in trained individuals (18-42 years of age), reaction time and working speed was improved immediately after a bout of cycling at 70% of their VO₂max, a workload that mimicked what they would cycle at for a one-hour all-out effort. Lambourne et al. (2006) found that in young adults (Means: 21.1 ± 1.7 years, VO₂max 37.33 ± 5.15 ml^.kg^-1.min^-1) who cycled for 40 minutes at a moderate intensity, cognition returned to baseline measurements 30-minutes post-exercise.

If attention is elevated after exercise, this may help an individual identify a stimulus, and then react. For example, if attention and reaction time are improved after exercise, this may help an individual be more alert during driving. If individuals, especially older adults, can pay more attention to events “on the road”, (e.g., deer suddenly crosses the road), they may more readily react and step on the brakes. Executive function, especially selective attention, is very important during driving; deterioration in selective attention results in an increased risk for crashes and decreases in driving ability (Adrian et al., 2011). More research is needed to determine the effects of differences in exercise intensities on cognition 30-minutes post-exercise in older adults.

One limitation that should be considered when interpreting the results of the current study is that VO₂max was estimated. This estimation may introduce a T10% error and could possibly mask differences between the moderate and high exercise intensities (Heyward, 2010). However, in the present study, cognition was improved regardless of exercise intensity in older women. More research needs to be completed with older adults to determine at what intensities increases in cognition might be elicited and what mechanisms (e.g., blood flow, neural activity, etc.) may contribute to these changes in reaction time and attention (Tsujii et al., 2013). Subsequent investigations may directly measure VO₂max and use indirect calorimetry to directly set varied exercise intensities. This is important because it is unknown whether the positive cognitive benefits after acute aerobic exercise in highly fit older adults are the same regardless of exercise intensity (Kamijo, 2009; Zervas et al., 1991). In addition, further research could be done to examine various recovery times (i.e., 15, 30, 60, or 120 minutes) and cognition after each of these intensities in older adults. In order to increase sample sizes, individuals on some medications may need to be included in future research designs.

This study was completed with older adult females because females may be at the greatest risk of developing cognitive decline because of the decrease in estrogen levels at menopause (Spirduso et al., 2008). It is believed that estrogen may have a protective effect on cognitive function in women. However, taking supplemental estrogen is not recommended because of the increased health risks (Asthana, 2004). All of the participants in this study were post-menopausal, but were moderately to highly active. Further research needs to be completed on older adult females to determine what other beneficial effects that aerobic exercise might have on cognition after exercise.