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Body armor effect on heat

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Body armor increases heat load on Soldier

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Body armor effect on heat

  1. 1. Impact of Body Armor on Physical Work Performance Colonel Ric Ricciardi 9 August 2006 9th Annual Force Health Protection Conference Albuquerque, New Mexico rricciardi@usuhs.mil
  2. 2. “Learning to care for those in harms way”
  3. 3. Co-Investigators  Laura Talbot, Ph.D, Ed.D., RN Associate Professor, GSN, USUHS  Patricia Deuster, Ph.D., M.P.H. Professor, Military and Emergency Medicine, USUHS
  4. 4. Special Thanks US Army Nurse Corps Study Participants from USN, USAF, USA and USPHS TriService Nursing Research Program Honorable Daniel K. Inouye The Henry M. Jackson Foundation for the Advancement of Military Medicine
  5. 5. Title of Study  The Impact of Body Armor on Physical Work Performance
  6. 6. Background  Personal Protective Equipment (such as body armor) when worn in high threat military environments impacts military personnel’s work performance  Decrements in Physical Performance impacts both mission and the individual  However little is known about the physiological effects of wearing body armor
  7. 7. Body Armor - Military Relevance  Reduces Lethality  Saves Lives  Prevents Injury References: Hoge, C. W., et al.(2004); Patel, T. H., et al., (2004); Mabry, R. L., et al., (2000).
  8. 8. January 7, 2006 Pentagon Study Links Fatalities to Body Armor MSNBC.com February 2006 U-S Soldiers Question Use of More Armor
  9. 9. Study Goal  Identify Physiological Risks associated with personal protective equipment such as body armor  Develop Strategies to Prevent or Mitigate Risks
  10. 10. Specific Aims  Determine changes in work performance, energy cost, and physiological fatigue as a function of body armor as compared to no body armor.  Compare how body armor alters energy cost and physiological fatigue under conditions of low and moderate physical activity levels.  Estimate how body composition and background variables such as age and sex affect:  work performance  energy cost  physiological fatigue
  11. 11. Central Hypothesis Individuals who wear body armor will have: Increased Energy Expenditure Increased Physiological Fatigue Reduced Work Performance
  12. 12. Conceptual Model of the Impact of Physical Load on Physical Performance Physical Load: Personal Protective Equipment (Body Armor) Energy Expenditure Physiological Fatigue Work Performance Physiological Risk
  13. 13. Overview of Study Design Counterbalance 16 Participants tested without body armor in first session 16 Participants tested with body armor in first session Same 16 Participants tested with body armor in second session Same 16 Participants tested without body armor in second session 32 Participants
  14. 14. Population  Healthy military personnel aged 18-40  Free of heart, endocrine and liver disease; hypertension; and asthma by history and physical exam  Nonpregnant  Able to perform treadmill exercise test  Able to wear body armor
  15. 15. Assessment of Energy Cost  Modified treadmill exercise using submax protocol at 4.5 and 9 MET’s.  Peak oxygen consumption (VO2peak) defined by highest 2 minute average, expressed in mL/kg/min
  16. 16. Assessment of Physiologic Fatigue  Blood Lactate  Borg Perceived Physical Exertion Scale  Heart Rate
  17. 17. Assessment of Work Performance  Scores on Physical Performance Battery  Heart Rate  Oxygen Consumption
  18. 18. Other Variables  Body adiposity approximated by body mass index (BMI) defined as weight in kg/ (height in meters)2  Anthropometric Measures  Bioelectrical Impedance Analysis
  19. 19. Procedures  Recruitment  Informed Consent  Counterbalance  Testing: 2 sessions with & without body armor  Treadmill Walking Test  Physical Performance Battery  Blood Analysis
  20. 20. Results
  21. 21. Aim 1 Determine changes in work performance, energy cost, and physiologic fatigue. Statistics  A paired-samples t-test was conducted to determine mean differences between the variables under two conditions (wearing and not wearing body armor).  Alpha level p<0.0025 (Bonferonni correction)
  22. 22. 0 10 20 30 40 50 Mean Oxygen Consumption 16.8 18.8 34.8 40.8 VO 2 (ml*kg -1 *min -1 ) VO 2 SP NBA VO 2 SP BA VO 2 MP NBA VO 2 MP BA * ** P < 0.001 12% 17%
  23. 23. 0 2 4 6 8 10 Mean Blood Lactate 1.74 1.74 3.96 6.66 9.59 8.78 mmol/L BL NBA BL BA PT NBA PT BA PPPB NBA PPPB BA * NS NS * P < 0.001 68%
  24. 24. 0 5 10 15 20 RPE SP NBA RPE SP BA RPE MP NBA RPE MP BA Mean Rating of Perceived Physical Exertion 8.35 10.4 14.3 16.6 BorgRPEScore * ** P < 0.001 16% 25%
  25. 25. 0 5 10 15 20 Hang Time NBA Hang Time BA Mean Hang Time 19.1 7.02 Seconds 63% * * P < 0.001
  26. 26. 0 2 4 6 8 10 Pull-Ups NBA Pull-Ups BA 9.12 3.59 NumberofRepititions Mean Number of Pull-Ups * P < 0.001 * 61%
  27. 27. 0 5 10 15 20 25 30 Step Test NBA Step Test BA Mean Step Count 28.7 24.3 StepCount * * P < 0.001 15%
  28. 28. 0 50 100 150 200 HR SP NBA HR SP BA HR MP NBA HR MP BA Mean Heart Rate 107 118 164 180 Beatsperminute * * * P < 0.001 10% 10%
  29. 29. 0 10 20 30 40 RR SP NBA RR SP BA RR MP NBA RR MP BA Mean Respiratory Rate 25.2 27.7 33.9 40 Breadthsperminute * P < 0.001 18% 10% * *
  30. 30. 0 0.2 0.4 0.6 0.8 1 1.2 RER SP NBA RER SP BA RER MP NBA RER MP BA 0.873 0.894 0.985 1.07 VCO 2 /VO 2 Mean Respiratory Exchange Ratio 8.6%* P < 0.001 * NS
  31. 31. Aim 2 Compare how body armor alters energy cost physiologic fatigue under conditions of low and moderate physical activity levels and whether that effect is the same in men and in women. Statistics  A one-way analysis of variance was conducted to determine mean differences between women and men under two conditions (wearing and not wearing body armor).  Alpha level p<0.05
  32. 32. Women (n = 17) Men (17) NBA BA p Percent Increase NBA BA p Percent Increase VO2 (mL∙kg-1 ∙min-1 ) 16.8 ± 1.4 18.9 ± 1.3 <0.001 12.5 16.8 ± 1.7 18.6 ± 2.0 <0.001 10.7 HR (beats/min) 109.1 ± 15.4 121.8 ± 17.0 <0.001 11.6 105.7 ± 14.0 114.9 ± 13.5 <0.001 8.7 R (VCO2 /VO2 ) 0.87 ± 0.1 0.88 ± 0.06 0.76 1.1 0.87 ± 0.05 0.91 ± 0.06 0.02 4.6 RR (breaths/min) 26.3 ± 4.8 29.7 ± 5.6 <0.001 12.9 24.0 ± 3.6 25.8 ± 3.4 <0.001 7.5 RPE 8.7 ± 0.1 11.0 ± 1.9 <0.001 26.4 8.7 ± 0.05 9.9 ± 1.4 <0.001 13.8 Physiological and Perceptual Response Values by Gender at Slow Pace
  33. 33. Physiological and Perceptual Response Values by Gender at Medium Pace Women (n = 17) Men (n = 17) NBA BA p Percent Increase NBA BA p Percent Increase VO2 (mL∙kg-1 ∙min-1 ) 33.6 ± 2.2 38.9 ± 3.3 <0.001 15.7 35.90 ± 4.8 42.6 ± 5.7 <0.001 18.6 HR (beats/min) 164.5 ± 14.9 179.0 ± 12.4 <0.001 8.8 162.5 ± 17.7 180 ± 14.5 <0.001 10.7 R (VCO2 /VO2 ) 0.97 ± 0.1 1.06 ± 0.14 <0.001 9.2 1.00 ± 0.1 1.06 ± 0.14 0.002 6.0 RR (breaths/min) 34.7 ± 5.5 40.9 ± 6.2 <0.001 17.9 33.2 ± 6.4 39.1 ± 7.1 <0.001 17.8 RPE 14.1 ± 2.2 16.8 ± 2.3 <0.001 19.1 14.4 ± 2.4 16.5 ± 2.0 <0.001 14.6
  34. 34. Women (n = 17) Men (n = 17) NBA BA p Percent Change NBA BA p Percent Change Baseline 1.5 ± 0.7 1.5 ± 0.7 0.7 NC 1.9 ± 0.9 2.0 ± 0.6 0.8 NC Post Treadmill 3.5 ± 2.4 6.0 ± 2.8 <0.001 71.4 4.4 ± 2.4 7.3 ± 2.4 <0.001 65.9 Post PPB 7.2 ± 2.7 7.5 ± 3.4 0.4 NC 11.9 ± 4.0 9.9 ± 3.1 0.01 16.9 Blood Lactate Levels by Gender
  35. 35. Aim 3  Estimate how body composition and background variables affect energy cost, physiological fatigue, and work performance.  To consider predictors of treadmill completion while wearing body armor, multivariate analyses using a logistic regression model were conducted on predictor variables (percent body fat, age, sex, rating of perceived physical exertion, and heart rate)
  36. 36. Logistic Regression Results Predictors of Test Completion  Physical Characteristics  Age, Waist Circumference, Percent Body Fat and BMI  Slow Pace  Heart Rate  Moderate Pace  Blood Lactate, RPE and Heart Rate  Physical Performance Battery  Pull-Ups
  37. 37. Logistic Regression Results – Body Fat *Body fat cut points = 17% in men and 26% in women Variable Variance Explained Specificity Sensitivity Body Fat* 20-26% 79% 67%
  38. 38. Logistic Regression Results – Slow Pace Variable Variance Explained Specificity Sensitivity Heart Rate 37-50% 80% 71%
  39. 39. Mean Heart Rate – Slow Pace without Body Armor Did not complete vs. completed testing Did not Complete Testing Completed Testing P Heart Rate (beats per minute) 118.0 ± 8.4 100.0 ± 13.5 <0.001
  40. 40. Logistic Regression Results – Moderate Pace RPE = Rating of Perceived Physical Exertion Variable Variance Explained Specificity Sensitivity Heart Rate 37-50% 80% 71% RPE 45-61% 90% 86% Lactate 56-75% 90% 92%
  41. 41. Mean Heart Rate, RPE and Lactate at Moderate Pace without Body Armor Did not complete vs. completed testing Did not Complete Testing Completed Testing P Heart Rate 173.57 ± 10.9 156.5 ± 15.6 0.001 RPE 16.1 ± 1.8 13.0 ± 1.5 <0.001 Lactate 6.1 ± 2.3 2.5 ± 0.9 <0.001 RPE = Rating of Perceived Physical Exertion
  42. 42. Logistic Regression Results Physical Performance Battery Variable Variance Explained Specificity Sensitivity Pull-Ups 48-65% 89% 75%
  43. 43. Mean Pull-Ups without Body Armor Did not complete vs. completed testing Did not Complete Testing Completed Testing P Pull-Ups 4.3 ± 3.9 12.5 ± 4.4 <0.001
  44. 44. Conclusions  The results of this study demonstrate that wearing interceptor body armor under simulated work conditions significantly: Increases energy cost Reduces physical work performance capabilities and Increases physiological fatigue
  45. 45. Conclusions  Of note, these physiologic changes occurred from a mean increase in body mass of only 15.7% (17.7% women and 14.1% men)  Nonlinear increases in VO2  Effect size 0.60 at the slow pace and 0.75 at the medium pace on VO2
  46. 46. Conclusions  The physical characteristic variable that was the best predictor of test completion in subjects wearing body armor was percent body fat. Lower body fat is associated with:  ↑ VO2peak  ↓ heart rate  ↑ pull-ups  ↓ rating of perceived physical exertion  ↓ Blood lactate levels (men)
  47. 47. Relationship between VO2 and Percent Body Fat at Medium Pace 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 VO2 MP NBA VO2 MP BA VO 2 (ml*kg -1 *min -1 ) Percent Body Fat R = 0.50 p= 0.004 R = 0.64 p< 0.001
  48. 48. Conclusions  The variable most predictive of treadmill test completion was blood lactate.  In field testing where blood analysis may not be available, the best predictor of test completion is heart rate at the slow (4.5 METs) or moderate pace (9 METs).
  49. 49. Recommendations  Body Composition Standards  Fitness Levels  Entry Requirements – age now 42 (NPS)  Caloric needs
  50. 50. Future Research  Thermoregulation  Field Studies  Specific to Military Related Occupational Specialties  Female Model of Body Armor – Related to chest pain complaints  Warrior Personal Protective System Model  Balanced Personal Protective System
  51. 51. Questions

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