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HQ U.S. Air Force Academy
I n t e g r i t y - S e r v i c e - E x c e l l e n c e
Acclimatization to Moderate Altitude: Red Cell
Mass & Performance
Jeff Nelson, Ph.D. USAFA Human Performance
Laboratory
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
USAFA for analysis oflong-term MA adaptation
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
Results: 1.5 mile AFT run time
†*†*†*
525
575
625
675
725
1.5 3 7 15 19 27 31
Chronic Alitude Exposure (months)
AF
T R
un T
ime
(sec
s)
MA
SL
C.
Legend: Significant (P < 0.01) main effects of altitude, time, & alt. x time interaction.
*, Significant difference between MA & SL; †, significant differences over time.
MA cadets ran 20-30s (4-5%) faster than SL cohorts
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Retro results: PFT (pull-ups, push-ups, sit-ups,
standing long jump) score
150
250
350
450
1.5 3 7 15 19 27 31
Chronic Altitude Exposure (months)
PF
T S
core
(poi
nts)
MA
SL
B.
Legend: Significant (P < 0.01) main effects of altitude & time; no altitude x time interaction!
MA cadets perform 6-7% better for 2+ yr than SL cohorts
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
Results: [Hb]
†‡†‡†‡*†§‡
13
14
15
16
17
18
Pre- USAFA (-6m)
AcuteUSAFA
(4d)
ChronicUSAFA(17m)
ChronicUSAFA(23m)
ChronicUSAFA(30m)
[Hb]
(g ·d
L -1)
MA
SL
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).
MA cadets’ 1.0 g/dL (6%) higher initially;SL cadets’ increased 1.5 g/dL (10%) with long-term MA exposure
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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
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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)
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Longitudinal Design
Time (weeks)Parameters Parameters examined:examined: (SL & MA)(SL & MA)
+.5+.5
(da(day4)y4)
+6+6 +8+8 +12+12 +15+15 +17 +17 to to +20+20
+23+23 +28+28 +30+30 +37+37 +42 +42 to to +45+45
+46+46
Hematological Hematological data:data:(CBC w/ retic. panel, (CBC w/ retic. panel, serum ferritin, sTfR, serum ferritin, sTfR, EPO)EPO)
XX XX XX XX XX XX XX
AFT & PFT:AFT & PFT:(part of USAFA fitness (part of USAFA fitness testing program)testing program)
XX XX XX
GXT:GXT:VOVO2peak2peak, power, sub-, power, sub-
max. economy & max. economy & [BLa], S[BLa], SaaOO22, etc., etc.
XX XX
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Cross-sectional Design
Time (weeks)Parameters Parameters examined:examined: (SL & MA)(SL & MA)
+.5+.5
(da(day4)y4)
+6+6 +8+8 +12+12
(+1(+1-3 -3 yrsyrs))
+15+15 +17 +17 to to +20+20
+23+23 +28+28 +30+30 +37+37
(+1(+1-3 -3 yrsyrs))
+42 +42 to to +45+45
+46+46
Hematological Hematological data:data:(CBC w/ retic. panel, (CBC w/ retic. panel, serum ferritin, sTfR, serum ferritin, sTfR, EPO)EPO)
XX XX XX XX XX XX XX
AFT & PFT:AFT & PFT:(part of USAFA fitness (part of USAFA fitness testing program)testing program)
XX XX XX
GXT:GXT:VOVO2peak2peak, power, sub-, power, sub-
max. economy & max. economy & [BLa], S[BLa], SaaOO22, etc., etc.
XX XX
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
Longitudinal/Cross-sectionalResults: AFT/PFT
490
540
590
640
690
6 12 30
Chronic MA Exposure (weeks)
AFT
Tim
e (s
ecs)
MA
SL
Legend: Significant (P < 0.05) main effects of altitude & time with no interaction.
****
500
540
580
620
660
Sem. 1 Sem. 2 Sem. 1 Sem. 2 Sem. 1 Sem. 2
Freshmen Sophomore Jr. & Sr.
USAFA Semester and Class Year
AF
T R
un
Tim
e (s
ecs)
MA
SL
Legend: Significant (P < 0.03) main effects of altitude & time;
*, significant (P < 0.05) differences between MA & SL.
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
Results: Cross-sectional hematological differences
†‡
14.5
15
15.5
16
16.5
17
17.5
18
Sem. 1 Sem. 2 Sem. 1 Sem. 2 Sem. 1 Sem. 2
Freshmen Sophomore Jr. & Sr.
[Hb]
(g·d
L-1)
MA
SL
[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.
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Results: VO2peak & economy
***
50
55
60
65
Sem. 1 Sem. 2 Sem. 1 Sem. 2 Sem. 1 Sem. 2
Freshmen Sophomore Jr. & Sr.
VO
2pea
k (m
L·k
g -1
·min
-1)
MA
SL** *
180
200
220
240
260
Sem. 1 Sem. 2 Sem. 1 Sem. 2 Sem. 1 Sem. 2
Freshmen Sophomore Jr. & Sr.
Subm
x. E
con.
(mL
· kg
-1· k
m -1
)MA
SL
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.
7.9% 5.2% 1.8%
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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 dataGenetic testing to assess individual variabilityN = 100 (20 MA, 80 SL; 50% Fe supplementation)
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THM determination via CO re-breathing
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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)
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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)
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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)
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THM Peak
Group Week THM % Increase
Fe 2+ 15 +73.7±39.4 g +10.4%
Placebo 28 +68.6±9.4 g +9.4%
Clearly, the iron group had a shorter acclimatization time
Hematological acclimatization is longer in duration than previously thought.
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
Indirect evidence of neocytolysis
Group THM loss (g) % of THM gained at MA
Male Iron -33.9±26.8 g -57.8%
Male Placebo -21.2±41.1 g -28.2%
Female Iron -25.7±15.7 g -41.4%
Female Placebo -18.6±20.9 g -33.7%
Winter break at sea level: ~3 weeksRange of total THM: 2.5%-4.0%Does exercise attenuate THM loss?
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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)
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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)
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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
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I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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
27/22
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Acknowledgments / Questions
USAFA Human Performance LaboratoryHQ USAFA / ADPH
2169 Field House Drive, Ste 111USAF Academy CO 80840
Jeff Nelson, Ph.D. [email protected]
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