Strength Training and Hemodynamic Responses to Exercise

Kevin R. Vincent, PhD, Heather K. Vincent, PhD, Randy W. Braith, PhD, Vineesh Bhatnagar, MD, David T. Lowenthal, MD, PhD

Disclosures

Am J Geriatr Cardiol. 2003;12(2) 

In This Article

Results

Sixty-two of the original 84 subjects completed the study (CON=16; LEX=24; HEX=22). Of the 22 who did not finish, 11 (CON=1, LEX=6, HEX=4) were dropped by the investigators for not adhering to the training protocol or dropped out voluntarily for reasons of inconvenience. The other 11 (CON=3, LEX=6, HEX=2) dropped out due to one of the following reasons: moved out of the area, financial difficulties, or surgery/injury (detached retina, atrial fibrillation, liver cancer, renal stenosis, prostate cancer) not related to the study protocol. Six of the training subjects experienced joint discomfort (three knee, two back, one elbow) and had to reduce training for 2 weeks. A total of 28 men and 34 women completed the study. The six subjects were distributed as follows: LEX group (one knee, one back), HEX group (two knee, one back, one elbow). To be included in the data analysis, participants in the two training groups must have completed >85% of the possible exercise sessions during the 6 month period. Participants participating in less than 85% of the sessions were deemed noncompliant and dropped from the study. Characteristics of those subjects who completed the study are listed by group in Table I . There were no statistically significant differences among groups for age, height, and weight either before or after the study (p≥0.05).

Muscle strength did not differ among groups at study entry. Muscular strength significantly increased (p<0.05) in both training groups ranging from 10.8%-25.3% and from 14.6%-27.6% for the LEX and HEX groups, respectively. Upper body strength was calculated as a composite of the five upper-body 1-RMs while lower-body strength was calculated as a composite of the three lower-body 1-RMs. Upper-body strength significantly increased (p=0.001) by 19.4% and 19.6% for the LEX and HEX groups, respectively. Lower-body strength significantly increased (p=0.001) by 17.9% and 21.1% for the LEX and HEX groups, respectively. Total strength values, calculated by summing the 1-RMs from the eight tested exercises increased significantly from pretraining to post-training (p=0.001), but were not different between the two training groups (17.2% and 17.8% for the LEX and HEX groups, respectively).

o2peak did not differ among groups at study entry, but significantly increased as a consequence of resistance training ( Table I ). Both the LEX (+23.5%) and HEX (+20.1%) groups significantly increased o2peak during the 6 months of resistance exercise (p=0.007). However, o2peak in the CON group did not change. Treadmill time to exhaustion during the GXT increased by 6.2%, 26.4%, and 23.3%, for the CON, LEX, and HEX groups, respectively. However, only the LEX and HEX groups significantly increased their treadmill time from pretest to post-test (p=0.04).

The resting HRs, blood pressures, and MAP in seated and standing positions are presented in Table II . The seated SBP values were significantly lower in the HEX compared to LEX group (p=0.04) following the training. MAP was significantly lower (p=0.04) following training for the HEX group.

To compare relative workloads, the times to complete the GXT were separated into quartiles. The HR, blood pressure, and MAP for each quartile of the GXT are found in Table III . Training was associated with higher DBP values in both LEX and HEX groups compared to CON at 50%, 75%, and 100% of the GXT (p<0.05). Also, the HEX group had higher HR values at 75% and 100% of the GXT compared to CON. There were no differences (p>0.05) in MAP values between groups at any point during the GXT. DBP was significantly lower at time points 0, 25, and 75 following training for the HEX group (p<0.05). DBP and MAP were significantly lower at time point 25 for the LEX group following training (p<0.05).

To compare cardiovascular responses at the same absolute workloads, the HR, blood pressure, and MAP for the first 8 minutes of the GXT are presented in Table IV . The HEX group demonstrated significantly lower (p<0.05) DBP and MAP after training. HR was lower for the HEX group at 2, 4, 6, and 8 minutes of the GXT. DBP was significantly lower (p<0.05) in the LEX group at the 2-minute time point.

The DBP response during the GXT can be seen in Figures 1 and 2. Figure 1 shows DBP at the GXT quartiles expressed as a ratio score with all time points divided by the 0 time point. This enables the DBP to be normalized since all groups are starting at the same value. This normalized figure demonstrates that the CON group has an inappropriate DBP response during the treadmill exercise. This inappropriate response is highlighted by a significant drop (p=0.02) in DBP from points 25 to 75. The ratio of exercise DBP/resting DBP is higher for both training groups at points 50-100 (p<0.05). A similar response is presented in Figure 2. Figure 2 shows the ratio score calculated as exercise DBP/resting DBP for the absolute workloads. Again, a decrease in DBP is evident for the CON compared to the HEX group (p<0.05).

Ratio of exercise diastolic blood pressure (DBP)/pre-exercise DBP measured at 0%, 25%, 50%, 75%, and 100% of a graded exercise test (GXT) for the control (CON), low-intensity exercise (LEX) and high-intensity exercise (HEX) groups. Figure displays post-training values.*p<0.05 vs. CON; †p<0.05 vs. CON.

Ratio of exercise diastolic blood pressure (DBP)/pre-exercise DBP measured at 0, 2, 4, 6, and 8 min of a graded exercise test for the control (CON), low-intensity exercise (LEX) and high-intensity exercise (HEX) groups. Figure displays post-training values.*p<0.05 vs. CON

The HEX group had lower (p<0.05) SBP at 3 and 5 min compared to LEX and CON ( Table V ). DBP values were lower (p<0.05) in HEX compared to LEX following the training. HR was significantly (p<0.05) lower post-training at 1, 3, and 5 minutes of recovery for the HEX group compared to pre-training values. HR was significantly (p<0.05) lower post-training at 1 and 5 minutes of recovery for the LEX group compared to pre-training values. There was a trend for the 3-minute time point to be lower in the LEX group post-training (p=0.06). MAP values were lower in the HEX group than in the LEX and CON grups at 1 and 3-minute post-exercise (p<0.05).

Peak exercise SBP, DBP, HR, and time to attain peak responses during the GXT are shown in Table I . Following the training, the LEX group had higher peak DBP values than CON (p=0.01); the HEX group had higher peak HR values than CON (p=0.004); peak DBP was significantly lower (p=0.04) in the HEX group compared to pre-training (91.7 vs. 95.5 mm Hg); and, lastly, both LEX and HEX significantly prolonged (p=0.01) their peak cardiovascular responses during the GXT by 2.5 and 4.7 min, respectively.

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