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Acclimatization to Moderate Altitude: Red Cell Mass & Performance

Acclimatization to Moderate Altitude: Red Cell Mass & Performance. Jeff Nelson, Ph.D. USAFA Human Performance Laboratory. Outline. Adaptation and acclimatization to moderate altitude via chronic residence at USAFA Lt Col Michael Brothers, Ph.D. – principal investigator Retrospective study

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Acclimatization to Moderate Altitude: Red Cell Mass & Performance

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  1. Acclimatization to Moderate Altitude: Red Cell Mass & Performance Jeff Nelson, Ph.D. USAFA Human Performance Laboratory

  2. Outline • Adaptation and acclimatization to moderate altitude via chronic residence at USAFA • Lt Col Michael Brothers, Ph.D. – principal investigator • Retrospective study • Longitudinal and cross-sectional studies • USAFA total hemoglobin mass altitude study • Individual variability, Neocytolysis, Iron supplementation • Summary

  3. Background • Limited data exists for adaptations occurring at moderate altitude (MA: 1,500-3,000m) despite the fact that ½ billion people reside at MA, & 100 million sojourn to MA annually • Individual variability • Neocytolysis • Iron Supplementation

  4. USAFA for analysis oflong-term MA adaptation

  5. USAFA for analysis oflong-term MA adaptation • Elevation = 2210m (7,250 feet) • Freshman students from all over the world (SL & MA) arrive w/in 24-hour period & in-process the same day each summer • Unique, well-controlled military environment: • Stringent physiological requirements for appointment • Limited travel away from USAFA until Thanksgiving (4-6 days) or Winter (2-3 week) break (+5.5 month MA exposure) • Rigorous physical training/testing programs all 4 years • Nearly identical diet

  6. Retrospective USAFA data • Examined pre-existing fitness (AFT/PFT) & blood data (H&H) of SL & MA cadets: • n = 2,147 male cadets (classes ’03 to ‘09) • SL < 153m / 500 ft: DE, FL, LA, MS, RI • MA >1500m / 5,000 ft: CO, WY

  7. Results: 1.5 mile AFT run time MA cadets ran 20-30s (4-5%) faster than SL cohorts Legend: Significant (P < 0.01) main effects of altitude, time, & alt. x time interaction. *, Significant difference between MA & SL; †, significant differences over time.

  8. Retro results: PFT (pull-ups, push-ups, sit-ups, standing long jump) score MA cadets perform 6-7% better for 2+ yr than SL cohorts Legend: Significant (P < 0.01) main effects of altitude & time; no altitude x time interaction!

  9. Results: [Hb] MA cadets’ 1.0 g/dL (6%) higher initially; SL cadets’ increased 1.5 g/dL (10%) with long-term MA exposure Legend: Significant (P < 0.005) main effects of altitude, time, & alt. x time interaction. Significant difference between MA & SL: § (P< 0.001), * (P < 0.01); Significant differences over time: Pre, † (P < 0.001); Acute, ‡ (P < 0.01).

  10. Retrospective Study • MA (USAFA: 2210m) exposure appeared to have an impact on SL cadets’ performance, & significantly increased [Hb] • Based on performance differences, acclimatization to MA appears to require 7+ months • Retrospective analysis prevents us from knowing if changes in performance are related to changes in blood…. • While hematological adaptations could account for aerobic differences, anaerobic differences are still evident after hematological acclimatization

  11. Long-term exposure to MA: Hematological & Physiological Adaptations • Subjects: 116+ male freshman – senior cadets • Freshman: 44+ (29 SL, 15 MA) • Sophomore: 30+ (18 SL, 12 MA) • Junior & Senior: 42+ (27 SL, 15 MA)

  12. Longitudinal Design Time (weeks)

  13. Cross-sectional Design Time (weeks)

  14. Longitudinal/Cross-sectionalResults: AFT/PFT Legend: Significant (P < 0.05) main effects of altitude & time with no interaction. Legend: Significant (P < 0.03) main effects of altitude & time; *, significant (P < 0.05) differences between MA & SL.

  15. Results: Cross-sectional hematological differences [Hb]: Significant (P < 0.03) main effect of class, & class x time interaction. †, significant (P < 0.05) between class; ‡, significant (P < 0.05) differences over time.

  16. Results: VO2peak & economy 5.2% 1.8% 7.9% Legend: Significant (P < 0.03) main effects of altitude & time, and significant (P < 0.05) alt. x class & alt. x time interactions occurred in sub-maximal running economy. *, Significant (P < 0.05) differences between MA & SL.

  17. USAFA THM Altitude Study • Consisted of early recruitment & baseline THM assessment (During In-processing) • Double blind, placebo control Fe supplementation w/ nine additional THM assessments (every 4-7 wks) • Additional VO2peak (3) & economy (5) tests at 3-5 velocities, w/ [BLa] & SaO2, plus AFT/PFT data • Genetic testing to assess individual variability • N = 100 (20 MA, 80 SL; 50% Fe supplementation)

  18. THM determination via CO re-breathing

  19. Acute hematological data • Altitude-related differences in erythrocyte (EV), plasma PV), and total blood (BV) volumes among male subjects #, sig. diff. between MA & SL subjects (p < 0.01) *, sig. diff. between MA & SL subjects (p < 0.05)

  20. Acute hematological data • Altitude-related differences in erythrocyte (EV), plasma PV), and total blood (BV) volumes among male subjects • Altitude-related differences in normalized THM among male subjects (no MA females able to be recruited) #, sig. diff. between MA & SL subjects (p < 0.01) *, sig. diff. between MA & SL subjects (p < 0.05)

  21. Chronic hematologicaldata: THM Male THM longitudinal data Significant main effect of time (p<0.001), Alt. (p<0.04), no effect of Fe (p=0.173), no interaction (p>0.38)

  22. THM Peak • Clearly, the iron group had a shorter acclimatization time • Hematological acclimatization is longer in duration than previously thought.

  23. Indirect evidence of neocytolysis Winter break at sea level: ~3 weeks Range of total THM: 2.5%-4.0% Does exercise attenuate THM loss?

  24. Chronic 1.5 mile run (AFT) performance Male AFT data Significant main effect of time (p<0.001), no effect of Fe (p = 0.59), Alt. (p=0.36), no interaction (p=0.83)

  25. Chronic 1.5 mile run (AFT) performance Female AFT data Significant main effect of time (p<0.001), no effect of Fe (p=0.422), significant interaction (p=0.049)

  26. Discussion, conclusions& application • Verified that hematological acclimatization requires longer time on average (~ 3-4 mo if Fe-replete; 4-6 wks possible if ‘fast’ responder, > 6 mo for ‘slow’ responders) • Fe supplement sig. improved female, but not male, adaptations; supplement dose insufficient? • De-acclimatization issues at winter break (neocytolysis)? • Ind. variability readily apparent—genetic analysis pending

  27. Main Points • Hematological acclimatization at MA takes longer than originally thought: 15-28 weeks, depending on genetics and/or iron availability • Performance acclimatization takes ~ 1.5 yrs in our cadet population • Importance in acknowledging neocytolysis in acclimatization time • Iron supplementation – importance to note toxicity potential if unmonitored; individual differences • Application

  28. Acknowledgments / Questions Thanks to: Lt Col Brandon Doan (Ph.D.), Lt Col Michael Zupan (Ph.D.), Mr. Al Wile (M.S.); Dr. Jeff Nelson, Dr. Bill Byrnes & Dr. Randy Wilber; Capt. Jules Macgregor, 2d Lt Andrea Pinchak, TSgt Chris Ruth, Ms. Christina Minares; Cadets Courtney Hemmert, Zach Garrett, Russell Smith, Jane Hwang, Robert Edmonds, Andrew Groberg, Chloe Angello, and Tyner Apt (former USAFA 499 researchers), Ms. Liz Terry, Mr. Ben Ryan, Ms. Darci Thurston, (HPL interns), plus all the USAFA cadet subjects! Funding: HQ USAF/SGSR, AFRL and USAFA HERC USAFA Human Performance Laboratory HQ USAFA / ADPH 2169 Field House Drive, Ste 111 USAF Academy CO 80840 Jeff Nelson, Ph.D. jeffrey.nelson@usafa.edu

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