Abstract
Eleven college age women (22.4 ± 2.21 years) volunteered to participate in this three-session experiment that investigated the acute physiological response to progressively increasing grades of treadmill walking while wearing a weighted vest.  The three experimental sessions consisted of walking at a treadmill speed of 4-km×hr-1 at grades of 0%, 4%, 8%, 12%, and 16% for five minutes at each level.  Subjects were randomly assigned to each of three treatments: walking with no vest (NV), walking with a 110% body weight (110%BW) load, and a 120% of body weight (120%BW) load.  Fifth minute data were evaluated statistically: heart rate (HR), oxygen uptake, minute ventilation, systolic blood pressure (SBP), and diastolic blood pressure (DBP).  ANOVA with repeated measures was used for statistical analysis.  Scheffe comparison determined significant differences between treatments.  The results showed that the addition of 20%BW stimulated a significant increase in heart rate (HR), oxygen uptake, minute ventilation, systolic blood pressure (SBP), at all inclines of walking over NV.  Yet, the increase in oxygen uptake amounted to an average of only one MET at each grade.  The increases in SBP and HR did not reach values considered to be abnormal for aerobic exercise. 
 

Several studies were found in the literature that evaluated the effects of weighted vest or weighted backpack exercise on health and fitness measures in the elderly.4 10 16 17 22  The focus of these studies dealt primarily with muscular strength improvement and bone density retention.  However, none of the studies noted in the present study evaluated the acute hemodynamic and or metabolic response to weighted vest exercise.  Only one study was found that evaluated the effects of training with added loads on oxygen uptake (VO₂₎ and strength in elderly women, but the study did not look at the acute response to added load exercise on hemodynamic or metabolic values 5.  The amount of added weight used in the studies cited ranged from 3%9 to 20%4 10 16 17 22. Given the potential health risks associated with the utilization of extremity-mounted weight, it seems logical that torso mounted weight is a safer alternative.  Yet, the health/risk benefits derived from exercising with torso-mounted weight are somewhat ambiguous.  Shoenfeld et al.18 reported a significant improvement in aerobic fitness from walking on a level surface with a backpack load of 3 kg at 5 km×hr-1 for three weeks that increased to 6 kg during the final week of training for health young men.  The authors concluded that the improvement in aerobic capacity was due to the backpack load and not the speed or duration of walking.  In another study, Engles et al.6 concluded that walking on a level surface at 4.8 km×hr-1 with a torso mounted weight equal to 4.5 kg. provided only a minimal increase in exercise intensity over walking without added weight for healthy men and women; and thus, its usefulness as a means of improving aerobic capacity is unlikely. 
 

Based on the review of literature presented here, it could be concluded that wearing torso-mounted weight can stimulate an improvement in muscular strength and endurance, and that such exercising will possibly benefit bone density retention;4 10 16 17 22 but it is unlikely that the added weight will elicit an improvement in aerobic capacity.  These assumptions are particularly useful for nurses, exercise scientists, and other rehabilitative and wellness professionals.  However, there is one important aspect in this area of research that has not been clearly defined; and that is the cardiovascular safety of exercising while wearing a torso-mounted weight.  Based on the results of studies that looked at torso-mounted weight versus extremity-mounted weight, it is likely that exercising with torso-mounted weight is safe.  Yet, no studies were found that specifically evaluated this hypothesis.  Therefore, the purpose of this study was to determine the acute hemodynamic and metabolic response to treadmill walking with torso mounted weight in young, healthy women.

Methods
 

Subjects 

Eleven, healthy college age Caucasian women (age = 22.4 ± 2.21 yrs; height = 162.05 ± 5.46 cm; weight = 58.76 ± 11.71 kg) volunteered for this study.  Initially, 20 young women volunteered for the study; but due to uncontrollable circumstances, nine elected to drop out of the investigation before the three data collection sessions were complete.  At the time of the study none of the subjects were involved in a formal physical fitness-training program for at least six months.  Young healthy female subjects were studied for safety reasons since no previous study had required subjects to engage in treadmill walking at continuously increasing inclines with 120% BW. This study met the requirements as set forth by the University’s Institutional Review Board on the use of human subjects. 
 

Experimental Design
The study was divided into four separate exercise sessions.  The first session was used to familiarize each subject with the exercise protocol and equipment, and to sign the informed consent.  During this session, subjects were instructed not to engage in any additional physical activity on the days testing was scheduled.  During the other three randomly assigned sessions, the subjects walked at 4.0-km×hr-1 at inclines of 0%, 4%, 8%, 12%, and 16% grade for five minutes each (total exercise time was 25 minutes).  The three experimental sessions differed in that the subjects either walked with no added weight or no vest (NV), 110% of their respective body weight (110%BW), or 120% of their respective body weight (120%BW).  Each subject performed the three experimental sessions during the same week with a 48-hour time elapse between each session.  A weight vest (All Pro Power Vest, Country Technology, Inc., Gays Mills, WI) was used as a means of carrying additional weight while exercising.

Measurements
Oxygen uptake (VO₂₎ and minute ventilation (V_E) were assessed continuously using an open circuit Quinton Q-PLEX 1 gas analyzer (Quinton Instrument Company, Seattle, WA).  Heart rate (HR) was measured using a Quinton Q4000 electrocardiograph.  Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured by auscultation using a Trimline mercuric sphygmomanometer (PyMaH Corporation, Somerville, NJ).  Fifth minute data for all measures were analyzed statistically.  It should be noted that maximum data (particularly max Oxygen uptake) were not collected because they were not considered necessary based on the stated purpose of the study.  Yet, in retrospect, not doing so might be considered a limitation of the study.

Statistical Analysis
The data were analyzed using ANOVA with repeated measures.  Scheffe comparison was used to determine significant differences between treatments.   A difference was considered significant at the P < 0.05 level.

Results

Oxygen Uptake
Descriptive statistics for (VO₂₎ are found in Table 1.  Oxygen uptake increased at all inclines of walking within treatments.  When comparing NV and 110%BW, statistical analysis identified a significant increase at walking inclines of 4%, 12%, and 16%Comparisons between 110%BW and 120%BW indicated a significant increase at 8% incline only.  The most obvious differences between treatments were between NV and 120%BW.  At every incline the difference was statistically significant.

Table 1.  Means, standard deviations, and significant differences for (VO₂₎ (ml×kg×min-1). 

Significant difference was set at the P < 0.05 level.

a = significant difference between NV & 110%BW

b = significant difference between NV & 120%BW

c = significant difference between 10%BW & 120%BW
 

Minute Ventilation
Descriptive statistics for V_E are found in Table 2.  Minute ventilation increased at all inclines of walking within treatments.  As might be expected, V_E followed much the same pattern as (VO₂₎ with respect to between treatment comparisons. 
 

Table 2.  Means, standard deviations, and significant differences for V_E (L×min-1) 

Significant difference was set at the P < 0.05 level.

a = significant difference between NV & 110%BW

b = significant difference between NV & 120%BW

c = significant difference between 110%BW & 120%BW

Heart Rate
Descriptive statistics for HR are found in Table 3.  Heart rate increased at all inclines of walking within treatments.  Significant increases in HR occurred between NV and 110%BW at walking inclines of 12% and 16%.  Between 110%BW and 120%BW, HR increased significantly at all inclines.  Likewise, the comparison between NV and 120%BW identified a significant increase at all inclines.

Table 3.  Means, standard deviations, and significant differences for HR (b×min-1)

Significant difference was set at the P < 0.05 level.

a = significant difference between NV & 110%BW

b = significant difference between NV & 120%BW

c = significant difference between 10%BW & 120%BW
 

Systolic Blood Pressure 
Descriptive statistics for SBP are found in Table 4.  Systolic blood pressure increased at all inclines of walking within treatments.  Systolic blood pressure increased significantly at 16% incline only, when NV and 110%BW were compared.  Inversely, there were significant differences between 110%BW and 120%BW at all inclines except 16%.  Systolic blood pressure increased significantly between NV and 120%BW at all inclines.
 

Table 4.  Means, standard deviations, and significant differences for SBP (mm Hg)

Significant difference was set at the P < 0.05 level.

a = significant difference between NV & 110%BW

b = significant difference between NV & 120%BW

c = significant difference between 110%BW & 120%BW
 

Diastolic Blood Pressure 
Descriptive statistics for DBP are found in Table 5.  Statistical analysis identified no significant change in DBP between treatments at any incline.
 

Table 5.  Means, standard deviations, and significant differences for DBP (mm Hg)

Significant difference was set at the P < 0.05 level.

a = significant difference between NV & 110%BW

b = significant difference between NV & 120%BW

c = significant difference between 110%BW & 120%BW

Discussion
The purpose of this study was to determine the acute hemodynamic and metabolic response to treadmill walking with torso mounted weight in young college age women.  The results indicated that when comparing NV and 110%BW, heart rate (HR), oxygen uptake, minute ventilation, and systolic blood pressure (SBP), all significantly increased, but not until the treadmill reached a 12% grade.  The only exception to this was in oxygen uptake.  There was a significant increase seen at 4% grade; but the increase became non-significant at an 8% grade.  It is difficult to determine why a consistent pattern of significant change among measured values did not occur until inclines of 12% and 16% grade were reached.  Possible reasoning could be due to fatigue resulting from the continuous walking protocol.  By the time the subjects reached the 12% grade, they had walked for 15 minutes.  Nonetheless, these findings seem to support the work of Engels et al., 6 who found that walking at a 0% grade at 4.8-km×hr-1 with a vest weight equal to 4.5 kg (~8%BW) failed to stimulate a significant increase in aerobic benefits of young male and female subjects.  The present study failed to stimulate a significant physiological response at grades of 0%, 4%, and  8%. Unlike walking with 110%BW, a consistent pattern of significant change did occur between NV and 120%BW.  A significant increase was noted in heart rate (HR), oxygen uptake, minute ventilation, and systolic blood pressure (SBP), at all grades. 

In this comparison the significant increases in (VO₂₎ at each incline amounted to 17%, 20%, 13%, 14%, and 15%, respectively.  However, these changes were calculated to be an average of approximately a one MET increase at each grade.  Due to this relatively small absolute increase noted in metabolically related values, the potential aerobic benefits derived from a training program utilizing 120%BW are uncertain.  As noted in the results, when comparing NV and 110%BW, HR did not increase significantly until an incline of 12% was reached; and SBP did not reach a significant level until a 16% grade was reached.  However, with only one exception, SBP and HR significantly increased at every incline between 110%BW and 120%BW. 
Yet, the same trend was not noted in (VO₂₎ and (V_E) between 110%BW and 120%BW.  A possible explanation for this is that the difference in response between hemodynamic values and metabolically related values was due to a greater utilization of fast-twitch muscle fibers at the heavier weight (i.e., 120%BW).  Rusko and Bosco15 concluded that when athletes trained with weight vests (~10%BW), fast-twitch muscle fibers were recruited at a lower intensity of exercise and earlier during prolonged submaximal training than when training without added loads.  They also noted that after four weeks of training there was a decrease in aerobic performance.

A concern with weight carried by hand or wrist method is that there is a probability that an abnormal hemodynamic response will result.  For example, Lind and McNicol 11 found no abnormal hemodynamic response when two men carried a medical stretcher weighing 82 kg at 3.2-km×hr-1 for 10 minutes using a shoulder harness.  Yet, when the same stretcher was carried using the hands, systolic and diastolic blood pressures and heart rate all increased significantly.  Although there were significant increases reported in SBP and HR in the present study, at no point did values exceed those which would be consider abnormal for a young, healthy female population.1  The fact that SBP and DBP responded normally to the exercise is particularly noteworthy since subjects reach 95% of their age predicted maximum HR at a 16% grade with 120%BW

Conclusion
Several conclusions were drawn from the results of this study.  First, the physiological data suggested that in a young, healthy, Caucasian female population, 110%BW while walking 4.0-km×hr-1 and 0% grade (level surface) is not sufficient to stimulate a significant increase in physiological activity when compared to walking without added weight.  Even when walking at grades of 4% and 8%, 110%BW did not result in significant change.  Second, when exercising at 120%BW a significant increase occurs at all inclines including a level surface (0% grade) over walking without additional weight.  However, the increase in exercise

(VO₂₎ averaged of only one MET at each incline walked.  Therefore, the benefits derived from utilizing a weight vest to stimulate significant improvements in aerobic capacity are uncertain, which tends to support previous findings.  Third, walking at 120%BW at a speed of 4.0-km×hr-1 on a treadmill at inclines up to 16% grade does not appear to elicit an abnormal hemodynamic response.  Therefore, its usefulness as a safe and effective rehabilitative or training device might have merit based on the results of the present study and others.10 16 17 22  Given the physiological change associated with the aging process, it would appear that the next step in this area of research is to clearly define the risk/benefit ratio of exercising with added torso-mounted weight in elderly subjects.  

References
 

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