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Original Research

The Acute Influence of Two Intensities of Aerobic Exercise on Strength Training Performance in Elderly Women

Lemos, Adriana1; Simão, Roberto1; Polito, Marcos2; Salles, Belmiro3; Rhea, Matthew R4; Alexander, Jeff4

Author Information
Journal of Strength and Conditioning Research: July 2009 - Volume 23 - Issue 4 - p 1252-1257
doi: 10.1519/JSC.0b013e318192b7c1
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Abstract

Introduction

The practice of regular aerobic and strength exercise by elderly people is recommended by the American College of Sports Medicine (3) because the interaction of morphological and functional variables such as hypertrophy and strength results in a healthy aging process (2,3). Increased strength can aid in the physical independence and functional capabilities of elderly populations and also reduce the risk of falling. Therefore, a strength training program involving large-muscle-group exercises performed 2-3 times per week in sessions involving 2-3 sets for each exercise is recommended for this age group (4). Improvements in strength, muscle hypertrophy, and mobility have been associated with this type of program among senior adults (10). As for aerobic exercise, it is recommended that it be performed 3 times per week for at least 20 minutes at an intensity of between 55 and 85% of maximum heart rate (HRmax), according to the subject's level of conditioning (4). Such exercise is necessary to maintain cardiovascular health and fitness.

However, training including aerobic and strength exercises performed in a single session, known in the literature as concurrent training, presents a specific challenge, especially among elderly populations. Fatigue generated from one mode of exercise may negatively influence the quantity and quality of exercise in the other mode. This issue has been studied in only 3 experiments with elderly people (14,24,25) focusing solely on chronic adaptations to concurrent training. None of these experiments was intended to verify the acute effects generated by aerobic training of different intensities on a subsequent strength training session with elderly women. If negative effects were seen with such practices, strategies would need to be developed and implemented to ensure that both aerobic and resistance exercise were effective.

Because both aerobic and strength activities are very important to elderly people as a way of improving their physical health and fitness, it is important to know the acute influence of different aerobic exercise intensities on strength performance. Therefore, the aim of the present study was to compare the acute influence of 2 aerobic exercise intensities on the number of repetitions performed during a subsequent strength training session by physically active elderly women.

Methods

Experimental Approach to the Problem

Data collection was performed on 5 alternate days. During the first visit to the laboratory, anthropomorphic measurements (height and weight) were taken and a treadmill test was completed. During the second and third days, 10-repetition maximum tests (10RM) were applied for the selected exercises (test and retest). On the final 2 days of data collection, strength training sessions after aerobic work at intensities of 60 or 80% HRmax were completed in a counterbalanced, crossover design.

Subjects

Twenty-five physically active women (age 74.3 ± 2.8 years; body mass 65.5 ± 5.2 kg; height 163 ± 5.9 cm) with at least 5 years of recreational strength and aerobic training experience participated in this study. All subjects had at least 5 years of experience performing leg press, leg extension, and leg curl exercise 2 or more days a week.

All subjects answered the Physical Activity Readiness Questionnaire (22) and signed an informed consent form before participating in the study. In accordance with the Declaration of Helsinki, the following exclusion criteria were adopted: a) use of medication affecting cardiovascular responses, b) existence of osteoarticular, and c) cardiovascular problems that might influence the performance of the proposed exercises.

Treadmill Test

Subjects were submitted to a cardiological evaluation that included a 12-lead resting electrocardiogram. Then, a graded-exercise test was performed on a treadmill. The Balke-Ware protocol was employed because the low progression stages are more appropriate for elderly subjects (4). The inclination of the treadmill was increased 1% every minute until the subject reached volitional exhaustion. Holding the side or front of the treadmill was not allowed, and the velocity was kept constant at 3.4 kph. During the test, heart rate and electrocardiogram were continuously monitored and stored in the software at the end of every minute. The following variables were monitored before and during each stage apart from the posttest: heart rate, blood pressure, rating of perceived exertion (RPE-Borg Scale CR10) (6,7), electrocardiogram, and clinical symptoms. Completion of this test provided accurate HRmax data for use when calculating aerobic training intensities.

Ten-Repetition Maximum Testing

Before completing the 10RM test (21), subjects completed 6 training sessions with the leg exercises and were instructed regarding proper completion of the testing. The mass of all weight plates used to measure 10RM was determined using a precision scale. Data were assessed during 2 nonconsecutive days. The 10RM tests were performed on the leg press at 45°(LP), leg extension (LE), and leg curl (LC). All machine exercises were performed on Personal Selection TechnoGym strength training equipment. To minimize possible errors in the 10RM tests, the following strategies were adopted: a) all subjects received standard instructions on the general routine of data assessment and on the exercise technique of each exercise before testing, b) during all testing sessions, the exercise technique of subjects was monitored and corrected as needed, and c) all subjects received standardized verbal encouragement during the tests (5).

During the 10RM test, each subject made a maximum of 3 attempts of each exercise with 5-minute rest intervals between attempts. After the 10RM load for a specific exercise had been determined, an interval of at least 20 minutes was allowed before the 10RM attempt for the next exercise. Standard exercise techniques were followed for each exercise. No pauses were allowed between the eccentric and concentric phases of a repetition or between repetitions. A complete range of motion for the exercise had to be completed for a repetition to be successful. Excellent day-to-day 10RM reliability for each exercise was obtained using this protocol (LP: r = 0.92; LE: r = 0.98; LC: r = 0.96). Additionally, a paired Student's t-test did not show significant differences between the 10RM tests for any of the exercises. The heaviest load achieved on both days was considered the 10RM.

Exercise Sessions

After obtaining the 10RM for each exercise, 2 training sessions within a 72-hour interval were performed in 2 sequential ways. Sequence A (SEQA) consisted of performing an aerobic training session on a treadmill for 20 minutes at 60% HRmax, followed immediately by a strength training session including 3 selected exercises (LP, LE, and LC), 3 sets per exercise, loaded with the resistance equal to the 10RM. In sequence B (SEQB), a similar procedure to SEQA was adopted including previous aerobic training on the treadmill at 80% HRmax. The exercise order adopted for the strength training was the same for both sequences: LP, LE, and LC. Counterbalanced crossover design was used to ensure that all subjects perform sequences SEQA and SEQB.

At the end of the aerobic training, each subject was asked to choose a value on the RPE (Borg CR10) scale to represent her level of perceived exertion (6,7). A 2-minute rest interval was allowed before beginning strength training. After the aerobic training at 60 or 80% HRmax, the volunteers performed 3 sets of each exercise until concentric failure, with a 90-second rest interval between sets and a 3-minute rest interval between exercises. The evaluator motivated the volunteers to help them reach the maximum number of repetitions until exhaustion. For each set, the maximum number of repetitions performed was recorded.

Standard instructions were provided to assess RPE immediately after completion of each aerobic and strength training exercise. Subjects were asked to use any number on the scale to rate their overall effort. A rating of 0 would be associated with no effort (rest), and a rating of 10 was considered to represent the maximum effort and was associated with the most stressful exercise sequence ever performed. All individuals were familiar with the Borg and OMNI-RES scales (16) because they had used each scale for 2 weeks during their normal sessions of testing and training. The OMNI-RES is a specific scale for strength exercises and has both verbal and mode-specific pictorial descriptors distributed along a comparatively narrow response range of 0-10 (16). The RPE observed in the OMNI-RES scale represents the rating of the perceived intensity after each exercise (3 sets) of the strength training session. After each aerobic session had been completed, the Borg scale was used to measure fatigue.

Statistical Analyses

A Shapiro-Wilk test was used to assess the data distribution, and the Levene test was performed to determine the homogeneity of variance. The number of repetitions in each set (inter- and intrasequence) after each aerobic intensity was analyzed using a repeated-measures analysis of variance (2 way), followed by a Tukey post hoc test for dependent samples. The total number of repetitions performed in all sets of each exercise, after the separate aerobic conditions, was analyzed using a paired Student's t-test. The results found for the RPE in the OMNI-RES and Borg scales were analyzed using the nonparametric Wilcoxon test. The level of significance was set at p ≤ 0.05 for all statistical procedures. Data are presented as mean ± SD. Statistical software was used for all analysis (version 6.0, Statsoft, Tulsa, Okla).

Results

The intrasequence comparison demonstrated similarities for all the exercises, regardless of the aerobic activity previously performed. In all cases, the numbers of repetitions throughout the sets decreased. Significant decreases (p < 0.05) were noted between the first (LP: 60% HRmax = 9.8 ± 0.5 reps, 80% HRmax = 8.9 ± 0.8 reps; LE: 60% HRmax = 9.3 ± 0.5 reps, 80% HRmax = 8.5 ± 0.9 reps; LC: 60% HRmax = 8.9 ± 0.4 reps, 80% HRmax = 7.3 ± 1.7 reps) and the second sets (LP: 60% HRmax = 9.0 ± 0.5 reps; 80% HRmax = 7.4 ± 0.9 reps, LE: 60% HRmax = 8.6 ± 0.5 reps, 80% HRmax = 7.1 ± 1.2 reps; LC: 60% HRmax = 8.4 ± 0.5 reps, 80% HRmax = 5.6 ± 1.4 reps), between the first and the third sets (LP: 60% HRmax = 8.5 ± 0.5 reps, 80% HRmax = 6.4 ± 1.7 reps; LE: 60% HRmax = 8.0 ± 0.5 reps, 80% HRmax = 5.9 ± 1.4 reps; LC: 60% HRmax = 7.6 ± 0.7 reps, 80% HRmax = 4.1 ± 1.4 reps) for all the exercises we evaluated, and between the second and third sets only after 80% HRmax.

The intersequence comparison demonstrated a difference (p < 0.05) in the number of repetitions during the exercises after the aerobic activity, with performance showing a greater decrease after the most intense aerobic exercise. Significant differences (p < 0.05) were found in the number of repetitions for each set when the exercises were compared, except for the first set of exercise LE. Figures 1-3 show a comparison of the numbers of repetitions in each set (intrasequence) and of the sum of the 3 sets of LP, LE, and LC, respectively, after the aerobic activity was performed at intensities of 60 and 80% HRmax.

F1-28
Figure 1:
Repetitions for each set of exercise leg press (LP) performed after aerobic activity at intensities of 60% maximum heart rate (HRmax; gray column) and 80% HRmax (striped column). Values are mean ± SD; differences at p < 0.05. *Significant difference in relation to the exercise performed after the 80% HRmax intensity; †significant difference in relation to the second and third sets of exercise performed after the aerobic activity at 60% HRmax intensity; ‡significant difference in relation to the second and third sets of exercise performed after the aerobic activity at 80% HRmax intensity; #significant difference in relation to the third set of exercise performed after the aerobic activity at 60% HRmax; §significant difference in relation to the third set of exercise performed after the aerobic activity at 80% HRmax.
F2-28
Figure 2:
Repetitions for each set of exercise leg extension (LE) performed after aerobic activity at intensities of 60% maximum heart rate (HRmax; gray column) and 80% HRmax (striped column). Values are mean ± SD; differences at p < 0.05. *Significant difference in relation to the exercise performed after the 80% HRmax intensity; †significant difference in relation to the second and third sets of exercise performed after the aerobic activity at 60% HRmax intensity; ‡significant difference in relation to the second and third sets of exercise performed after the aerobic activity at 80% HRmax intensity; #significant difference in relation to the third set of exercise performed after the aerobic activity at 60% HRmax; §significant difference in relation to the third set of exercise performed after the aerobic activity at 80% HRmax.
F3-28
Figure 3:
Repetitions for each set of exercise leg curl (LC) performed after aerobic activity at intensities of 60% maximum heart rate (HRmax; gray column) and 80% HRmax (striped column). Values are mean ± SD; differences at p < 0.05. *Significant difference in relation to the exercise performed after the 80% HRmax intensity; †significant difference in relation to the second and third sets of exercise performed after the aerobic activity at 60% HRmax intensity; ‡significant difference in relation to the second and third sets of exercise performed after the aerobic activity at 80% HRmax intensity; #significant difference in relation to the third set of exercise performed after the aerobic activity at 60% HRmax; §significant difference in relation to the third set of exercise performed after the aerobic activity at 80% HRmax.

The RPE demonstrated a significant difference (p < 0.05) for the strength training session after aerobic activity of both 80 and 60% HRmax (Figure 4), signifying increased fatigue. The RPE after the aerobic training session (Figure 5) at 80% HRmax was significantly higher (median 8) than the one found for aerobic training performed at 60% HRmax (median 6).

F4-28
Figure 4:
Perceived exertion after each exercise performed after aerobic activities at 60% maximum heart rate (HRmax; gray column) and 80% HRmax (striped column) intensities. Median values. *Significant difference in relation to the exercise performed after intensity of 80% HRmax.
F5-28
Figure 5:
Perceived exertion after aerobic activity at 60% maximum heart rate (HRmax; gray column) and 80% HRmax (striped column) intensities. Median values. *Significant difference in relation to intensity at 60% HRmax.

Discussion

Overall, this study demonstrates that the volume of a resistance training session is hampered by the performance of aerobic exercise immediately beforehand. The higher the intensity of the aerobic exercise, the greater the decrease in the number of repetitions performed in each set of resistance training. Thus, aerobic and resistance training performed concurrently in an acute exercise bout has a negative influence on resistance training performance among elderly women. A pilot study previously carried out (17), using methods similar to those of the present experiment and involving only 8 volunteers ages 60-75, showed results similar to those from this experiment for the intersequence comparison.

During the present experiment, the greatest decrease in intrasequence performance, measured in the same workout, was certainly influenced by the higher-effort intensity generated by the aerobic activity, which also showed higher RPE values after the aerobic activity and also after the 3 sets of each exercise. It is worth highlighting, however, that the interference caused on the number of repetitions in each set per exercise was attributable not only to the fatigue mechanisms caused by the previous aerobic activity but also to the effect of the fatigue caused by performing each set. The negative effect on the performance of strength training attributable to the number of repetitions may be related to the residual fatigue caused by demands on the same muscle groups by both training modalities.

Among the peripheral causes of acute residual fatigue, the accumulation of metabolites (inorganic phosphate, lactic acid, ammonia) and the depletion of energy substrates such as adenosine triphosphate, creatine phosphate, and muscle glycogen may account for such fatigue. High levels of lactate in the blood are commonly found after high-intensity resistive exercises (18). Such factors may be responsible for altering the excitation-contraction process, changing the capacity to produce tension of the muscle involved in the exercise.

Leveritt et al. (19) have demonstrated that different mechanisms of adaptation to aerobic training have helped inhibit strength development in young people, and they associate the phenomena they observed with the chronic or acute hypothesis. The acute hypothesis states that strength training is affected by the residual fatigue of the previous aerobic training bout (8). The physiological mechanisms that produce the residual fatigue associated with the acute hypothesis seem to be related to the training parameters used in the type of aerobic exercise (18). Thus, it is implied that such inhibitory effects commonly found in the literature may be associated with aerobic activities of long duration and intensity (8,19).

These results should be taken into account when optimizing responses to strength training, because decreases in training volume may counteract strength and hypertrophy gains, as already demonstrated in studies about concurrent training (9,11-13,15). Sporer and Wenger (23) have observed that after different recovery periods during 2 different types of aerobic training performed using an ergometric cycle, there was a reduction in the total volume of repetitions at 75% 1RM in the leg press. However, the same decrease was not seen in the bench press exercise. Thus, the residual fatigue brought about by aerobic conditioning seems muscle specific.

Leveritt et al. (19) acknowledge the acute effect of high-intensity aerobic training over the subsequent strength training including squat and leg extension exercises. The aerobic training was performed on an ergometric cycle from 40 to 100% of peak o2. The squat exercise included 3 sets at 80% 1RM, whereas the leg extension in the isokinetic equipment consisted of 1RM performed at 5 different execution velocities. The study found significant decreases for both exercises.

The results found here confirm the findings of Abernethy (1), who verified the influence of 2 types of aerobic training, continuous of low intensity and high intensity with intervals, in a strength test performed after the leg extension exercise using isokinetic equipment. Strength was evaluated for 10 velocities of maximum contractions. Both modalities of previous aerobic training significantly decreased the number of subsequent maximum contractions.

The results of the present study suggest that 90 seconds of rest between sets, and 2 minutes of rest between exercises, were not sufficient to keep the maximum number of repetitions using the weights obtained with the 10RM test. Such behavior was observed in all exercises, being more easily identified after the aerobic training at 80% HRmax. If lengthier rest periods were allotted, the negative influence on training volume may have been avoided. Therefore, if aerobic exercise is to be performed before resistance training, longer rest periods should be allowed to maintain the desired volume of training.

One potential weakness of the current study is that it did not include exercise conditioning of 3 resistance sets with no aerobic exercise. This condition would have allowed the determination of the exact amount of decrease in performance attributable to the fatigue of the aerobic conditions, as compared with muscular fatigue, from each set. However, this omission does not alter the finding that the aerobic exercise showed a decrease in resistance training performance.

The health and fitness benefits for elderly women that can be garnered from a well-designed resistance training program can have a profound effect on the length and quality of life. As exercise professionals design programs to facilitate this training and enhance functionality, it is important that they consider the residual effects of fatigue if aerobic exercise is performed before resistance exercise. It is unclear whether resistance training performed before aerobic exercise would have a negative effect, and more research should be conducted accordingly; however, when possible, it seems that elderly women should focus on one fitness component per exercise session. This would allow for a higher quantity-and, most likely, quality-of both modes of training without the negative effects of fatigue.

Practical Applications

According to the data obtained, both 60 and 80% HRmax performed for 20 minutes before resistance training have a negative effect on the volume of each subsequent set. Exercise professionals should consider the effects of fatigue on elderly women when designing and implementing concurrent aerobic and strength training exercises. If significant strength improvements are needed, aerobic exercise should be performed in a separate training session to allow for greater volumes of resistance training. If training is not separated, lengthier rest periods between sets and exercises should be allotted to prevent as much of the negative effect of fatigue as possible.

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    Keywords:

    strength training; resistive exercises; performance; concurrent training; fatigue

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