EFFECTS OF GENDER, AGE, CIRCADIAN RHYTHMS, AND SLEEP LOSS ON THERMAL RESPONSES DURING EXERCISE

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EFFECTS OF GENDER, AGE, CIRCADIAN RHYTHMS, AND
SLEEP LOSS ON THERMAL RESPONSES DURING EXERCISE
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REVIEW

• HUMAN ORGANISM IS A REGULATING ORGANISM GOVERNED
  BY A PROPORTIONAL CONTROL SYSTEM GRADED
  RESPONSE TO A SIGNAL WHICH INCREASES OR DECREASES
  IN PROPORTION TO THE INTENSITY OF THE STIMULUS.

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REVIEW

• THRESHOLD - TEMPERATURE ABOVE WHICH OR BELOW
  WHICH EFFECTOR RESPONSE IS DIFFERENT FROM THE
  BASELINE RESPONSE AT REST.
• SLOPE (GAIN) OR THERMOSENSITIVITY - DIFFERENCE IN
  EFFECTOR RESPONSE PER UNIT OF CHANGE IN CORE
  TEMPERATURE.

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GENDER DIFFERENCES IN THERMOREGULATION
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GENDER DIFFERENCES RELATED TO THE MENSTRUAL CYCLE
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• FOLLICULR PHASE
• FOLLICLE STIMULATING HORMONE (FSH) OF ANTERIOR
  PITUITARY STIMULATES DEVELOPMENT OF FOLLICLES
  (OVA), WHICH SECRETE INCREASING AMOUNTS OF
  ESTROGEN AND EVENTUALLY SMALL AMOUNTS OF
  PROGESTERONE.

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• INCREASED ESTROGEN STIMULATES
• PROLIFERATION OF UTERUS ENDOMETRIUM (MUCOUS
  MEMBRANCE OF UTERUS).

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• INCREASED ESTROGEN STIMULATES
• SECRETION OF LHRF FROM HYPOTHALAMUS, WHICH
  STIMULATES INCREASED RELEASE OF LH AND FSH
  (13TH-15TH DAY) FROM ANTERIOR PITUITARY
  INCREASED LH LEVELS STIMULATE FOLLICLES TO MATURE
  AND BREAK THROUGH THE OVARIAN WALL 14-24 HOURS
  AFTER THE LH SURGE (OVULATION).

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• LUTEAL PHASE
• SUPPORTING STRUCTURE OF FOLLICLES FORM CORPUS
  LUTEUM (YELLOW GLANDULAR MASS IN OVARY FORMED BY
  THE OVARIAN FOLLICLES), WHICH STIMULATES
  PROGESTERONE SECRETION THAT INDUCES SECRETORY
  CHANGES IN THE UTERUS.
• LH AND FSH SECRETION DECREASES.

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• IF FERTILIZATION DOES NOT OCCUR, THE CORPUS
  LUTEUM DEGENERATES RESULTING IN DECREASED
  PROGESTERONE SECRETION, WHICH LEADS TO
  ENDOMETRIUM DEGENERATION AND MENES BEGINS.

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• NOTE THERE ARE HIGHER CORE TEMPERATURES
  (0.4oC) DURING THE LUTEAL PHASE OF THE
  MENESTRUAL CYCLE WHEN PROGESTERONE LEVELS ARE
  ELEVATED. ALSO, DURING THE ENTIRE MENSTRUAL
  CYCLE, CORE TEMPERATURES ARE HIGHER THE PM THAN
  DURING THE EARLY AM.

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• ELEVATION OF CORE TEMPERATURE OF ABOUT 0.4o C
  DURING LUTEAL PHASE EFFECTS THERMOREGULATORY
  SET POINT IN TWO WAYS
• EARLIER ONSET OF SHIVERING AND HEAT
  PRODUCTION (I.E., HEAT CONSERVING MECHANISMS).
• INCREASED CORE TEMPERATURE THRESHOLD FOR
  ONSET OF HEAT LOSS MECHANISMS SUCH AS SWEATING
  AND CUTANEOUS VASODILATION. HEAT LOSS
  MECHANISMS DO NOT BEGIN UNTIL HIGHER CORE
  TEMPERATURE IS REACHED.

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• NOTE PARALLEL CHANGES IN SUDOMOTOR (SWEATING)
  AND VASOMOTOR (VASODILATION) RESPONSES INDICATES
  THAT THERE IS A CENTRAL ALTERATION IN
  THERMOREGULATORY CONTROL WITHIN THE HYPOTHALAMUS.

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• ELEVATION OF CORE TEMPERATURE OF ABOUT 0.4o C
  DURING LUTEAL PHASE INCREASES THE CORE
  TEMPERATURE AT WHICH THERMAL COMFORT IS
  PERCEIVED, WHICH MAY IN PART BE RELATED TO THE
  SLIGHTLY HIGHER SKIN TEMPERATURES OBSERVED DURING
  THE LUTEAL PHASE.

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WORK-HEAT TOLERANCE
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• BEFORE HEAT ADAPTATION, HEAT STORAGE IS INCREASED
  DURING THE LUTEAL PHASE DUE TO DELAYED ONSET OF
  SWEATING AS THE THRESHOLD FOR ONSET OF SWEATING
  IS INCREASED ALSO, SWEATING SENSITIVITY MAY ALSO
  BE SUPPRESSED DUE TO
• INCREASED EFFECTS OF HIDROMEIOSIS (??).
• DECREASED SHIFT OF FLUID OUT OF THE VASCULAR
  COMPARTMENT AS HEMOCONCENTRATION OCCURS LESS
  RAPIDLY IN THE LUTEAL PHASE.

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• AFTER HEAT ADAPTATION, MENSTRUAL CYCLE HAS
  MINIMAL EFFECTS ON THE WORK-HEAT TOLERANCE OF
  WOMEN DURING EITHER THE FOLLICULAR OR LUTEAL
  PHASE HEAT ADAPTATION BRINGS ON FASTER SWEATING
  RESPONSE BY DECREASING THE CORE TEMPERATURE
  THRESHOLD FOR THE ONSET OF SWEATING SWEATING
  SENSITIVITY MAY ALSO BE IMPROVED BUT IT DOES NOT
  FURTHER INCREASE SENSITIVITY INDUCED BY TRAINING.
  HEAT ADAPTATION ALSO DECREASES THE THRESHOLD FOR
  THE ONSET OF SKIN (CUTANEOUS) BLOOD FLOW AND
  INCREASES THE SENSITIVITY OF THE SKIN BLOOD FLOW
  RESPONSE.

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• ALSO, TRAINING DECREASES THE THRESHOLD FOR THE
  ONSET OF SWEATING AND INCREASES THE SENSITIVITY
  OF THE SWEAT RATE RESPONSE. TRAINING ALSO
  DECREASES THE THRESHOLD FOR THE ONSET OF SKIN
  (CUTANEOUS) BLOOD FLOW.

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GENDER DIFFERENCES
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• PERFORMANCE OF LOW INTENSITY EXERCISE IN BOTH DRY
  AND WET ENVIRONMENTAL CONDITIONS ELICITS QUITE
  SIMILAR RESPONSES IN BOTH FEMALES AND MALES,
  PARTICULARLY IF FACTORS SUCH AS BODY SURFACE
  AREA, FITNESS LEVEL, BODY COMPOSITION, BODY SIZE,
  AND MENSTRUAL CYCLE PHASES ARE CONTROLLED.

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• HOWEVER, DURING THE LUTEAL PHASE OF THE MENSTRUAL
  CYCLE WHEN CORE TEMPERATURE IS ELEVATED AND HEAT
  STORAGE IS INCREASED, PERFORMANCE MAY BE LIMITED
  DURING HIGH INTENSITY PERFORMANCE UNDER CERTAIN
  HYPERTHERMIC CONDITIONS.

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CARDIORESPIRATORY FITNESS LEVEL (I.E., MAXIMAL
OXYGEN UPTAKE RATE) AND HEAT TOLERANCE
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• BOTH FEMALE AND MALE RESPONSES TO HEAT STRESS
  APPEAR TO BE HIGHLY DEPENDENT ON FITNESS LEVEL
  FOR EXAMPLE, VO2MAX IS SINGLE BEST DETERMINANT OF
  DIFFERENCES IN SWEAT SECRETION PRODUCED BY AN
  INCREASE IN CORE TEMPERATURE. ALSO, INDIVIDUALS
  WITH A HIGH MAXIMAL OXYGEN UPTAKE RATE HAVE A
  LOWER STEADY-STATE CORE TEMPERATURE DURING HEAT
  STRESS AND CAN ADAPT TO HEAT STRESS FASTER (I.E.,
  FEW DAYS) AS EVIDENCED BY A EARLIER PLATEAU IN
  CORE TEMPERATURE DURING LONG-TERM HEAT EXPOSURE.

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AGE AND HEAT TOLERANCE
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AGE AND HEAT TOLERANCE
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OLDER ADULTS - LOWER HEAT TOLERANCE
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• DECREASED BLOOD VOLUME.
• INCREASED BODY FAT.
• LOWER FITNESS LEVEL (VO2MAX), WHICH RESULTS IN A
  LOWER LEVEL OF SWEAT SECRETION FOR A GIVEN
  INCREASE IN CORE TEMPERATURE, HIGHER STEADY-STATE
  TC, AND DECREASED ABILITY TO ADAPT
• TO HEAT STRESS.

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• LOWER CARDIAC OUTPUT DUE TO LOWER STROKE VOLUME
  AND LOWER MAXIMAL HEART RATE.
• INCREASED POTENTIAL FOR CARDIOVASCULAR STRAIN.
• THRESHOLD FOR ONSET OF SWEATING AND SWEATING
  SENSITIVITY (??).

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• DECREASED SWEATING CAPACITY DUE TO A DECREASE IN
  TOTAL BODY WATER.
• DECREASED CONVECTIVE, EVAPORATIVE, AND RADIANT
  HEAT LOSS.
• REDUCED ABILITY TO ADAPT TO HEAT.

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YOUTH - LOWER HEAT TOLERANCE
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• LOWER B0DY SURFACE AREA (BSA).
• GREATER BSA/BW RATIO WHICH INCREASES THE
  POTENTIAL FOR
• HEAT LOSS IF AIR TEMPERATURE IS LESS THAN SKIN
  TEMPERATURE OR INCREASES THE POTENTIAL FOR HEAT
  GAIN IF AIR TEMPERATURE IS GREATER THAN SKIN
  TEMPERATURE. ALSO, INCREASES THE GRADIENT FOR
  RADIANT HEAT GAIN.
• LOWER BLOOD VOLUME.

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• HIGHER PERCENT BODY FAT.
• HIGHER THRESHOLD FOR ONSET OF SWEATING (??).
• SWEATING SENSITIVITY (??).
• POSSIBLY A DECREASED CAPACITY FOR SWEATING DUE
  LOWER TOTAL BODY WATER.

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• LOWER SWEATING RATE AT REST AND DURING EXERCISE,
  WHICH POTENTIALLY LOWERS THE CAPACITY FOR
  EVAPORATIVE HEAT COOLING.
• GREATER ENERGY EXPENDITURE DURING WALKING AND
  RUNNING FOR A GIVEN ABSOLUTE WORKLOAD, WHICH
  RESULTS IN GREATER METABOLIC HEAT PRODUCTION PER
  KILOGRAM OF BODY WEIGHT.
• REDUCED ANATOMICAL VOLUME OF HEART AND REDUCED
  STROKE VOLUME.

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• INCREASED POTENTIAL FOR CARDIOVASCULAR STRAIN.
• LOWER CARDIAC OUTPUT AT A GIVEN METABOLIC LEVEL,
  WHICH LOWERS THE CAPACITY FOR CONVECTIVE HEAT
  TRANSFER FROM THE BODY CORE TO THE PERIPHERAL
  SKIN.

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• DECREASED POTENTIAL FOR CONVECTIVE, EVAPORATIVE,
  AND
• RADIANT HEAT LOSS.
• REDUCED ABILITY TO ADAPT TO THE HEAT.
• HIGHER BASAL METABOLIC RATE WHICH RESULTS IN
  GREATER RELATIVE HEAT PRODUCTION.

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CIRCADIAN RHYTHMS
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ZEITGEBERS

• EXTERNAL RHYTHMIC INFLUENCES THAT PROVIDE TIME
  CUES, WHICH SYNCHRONIZE CIRCADIAN RHYTHMS WITHIN
  AN INDIVIDUAL.
• NORMAL SYSTEMS OSCILLATE IN A 24 HOUR CYCLE.

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ZEITGEBERS

• WITHOUT ZEITGEBERS, CIRCADIAN RHYTHMS BECOME FREE
  RUNNING
• - CORE TEMPERATURE FOLLOWS 25 HOUR CYCLE.
• - SLEEP/WAKE 25 HOUR CYCLE.

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EXAMPLES OF EXTERNAL RHYTHMIC INFLUENCES

• LIGHT/DARK CYCLE.
• SLEEP/WAKEFULNESS CYCLE.
• SOCIAL ACTIVITY.
• FEEDING/FASTING CYCLE.

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TWO PACEMAKERS

• X - LIGHT DARK/CYCLE (4 TIMES AS STRONG) WILL
  OVER-RIDE OR CONTROL Y PACEMAKER BECAUSE IT IS
  FOUR TIMES AS STRONG.
• Y - FEEDING/FASTING AND ACTIVITY CYCLE.

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EFFECTS ON THERMOREGULATION
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• CIRCADIAN RHYTHMS CHANGE CORE TEMPERATURE
  THRESHOLD FOR THE ONSET OF SUDOMOTOR (I.E.,
  SWEATING) AND VASOMOTOR (I.E., BLOOD FLOW)
  RESPONSES.
• AS LONG AS HEAT LOSS EFFECTOR MECHANISMS (I.E.,
  SWEATING AND VASODILATION OF THE SKIN
  VASCULATURE) ARE TIGHTLY COUPLED TO CORE
  TEMPERATURE RHYTHM, THERE IS NO EVIDENCE THAT THE
  CIRCADIAN CYCLE IMPAIRS THE HOMEOSTATIC
  MECHANISMS OF THERMOREGULATION.

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• THRESHOLDS FOR ONSET OF SWEATING AND VASODILATION
  OF SKIN VASCULATURE TEND TO BE HIGHER IN THE PM
  THAN THE EARLY AM DUE TO CIRCADIAN MODULATION OF
  THERMOREGULATORY SET POINTS BY THE X PACEMAKER.
• CHANGES IN THRESHOLDS FOR SUDOMOTOR (SWEATING)
  AND VASOMOTOR (SKIN BLOOD FLOW) RESPONSES
  REGULATE CIRCADIAN RHYTHM CHANGES IN CORE
  TEMPERATURE.

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Jehue et al. (1993). Effect of time zone and
game time changes on team performance. Medicine
and Science in Sports and Exercise, 25, 127- 131.
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• Among all intra-time zone rivals, home teams won
  56 and away teams won 44 on the games between
  1978-1987 in the NFL.

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• For West coast teams, trans-meridian travel
  decreased the winning percentages by 14 when
  playing Central teams and 16 when playing East
  coast teams when traveling 42 hr pre-game
  however, for one West coast team which advanced
  practice time 3 hr and traveled 48 hr prior to
  the game, their winning percentage against East
  coast teams was actually 2 higher than expected.

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• For night games, West coast teams had a high home
  winning percentage when playing Central (75) and
  East coast (68) teams, with little or no fall in
  away winning percentage (68 versus Central teams
  and 69 versus East coast teams). For Central
  and East coast teams, playing late at night in
  the West resulted in the game occurring in early
  morning hours when many body rhythms approach
  their daily low. For West coast teams, the night
  games played in Central and East areas resulted
  in the game occurring at a time similar to West
  coast practice time.

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Practical Recommendations

• Travel at least 48 hr and preferably 72 hr or
  more (??) prior to the game or event.
• Adjust practice time to the time zone in which
  the upcoming game or event is going to occur.
• In order for circadian rhythms to completely
  adjust, allow 24 hr for each time zone crossed.

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SLEEP LOSS
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TYPES OF SLEEP
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SLOW WAVE SLEEP, DREAMLESS SLEEP, DELTA WAVE
SLEEP, OR NORMAL SLEEP

• VERY RESTFUL.
• DECREASED VASCULAR TONE.
• DECREASED VEGETATIVE FUNCTIONS.
• 10-30 DECREASE IN BLOOD PRESSURE,
  RESPIRATORY RATE, AND BASAL METABOLIC RATE.

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PARDOXICAL SLEEP OR RAPID EYE MOVEMENT (REM) SLEEP

• OCCURS EVERY 90 MIN FOR 5-20 MIN.
• INCREASED TIREDNESS WILL DECREASE REM SLEEP.
• AS ONE BECOMES MORE RESTED DURING THE NIGHT, THE
  DURATION OF REM SLEEP INCREASES.

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REM SLEEP IS ASSOCIATED WITH

• ACTIVE DREAMING.
• DEEPER, MORE SOUND SLEEP GREATER DIFFICULTY TO
  AWAKE PERSON IN REM SLEEP.
• DECREASED MUSCLE TONE DUE TO STRONG INHIBITION OF
  THE NEURAL PATHWAYS FROM THE RETICULAR ACTIVATING
  SYSTEM.

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REM SLEEP IS ASSOCIATED WITH

• RESTORATIVE PROCESS.
• IRREGULAR HEART RATE AND RESPIRATORY RATE.
• SOME IRREGULAR MUSCLE MOVEMENT SUCH AS RAPID EYE
  MOVEMENT (REM).

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REM SLEEP IS ASSOCIATED WITH

• ACTIVE BRAIN PATTERNS.
• MAY ENHANCE THE CONSOLIDATION OF LONG-TERM
  MEMORY.

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• REM SLEEP INHIBITS SUDOMOTOR (I.E. SWEATING)
  RESPONSES RESULTING IN AN INCREASE IN CORE
  TEMPERATURE NO IMPACT ON VASOMOTOR (I.E., BLOOD
  FLOW) RESPONSES.
• SWS SLEEP ASSOCIATED WITH HIGHEST SWEAT RATE IN A
  WARM ENVIRONMENT AND HENCE A DECREASE IN CORE
  TEMPERATURE.

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SLEEP LOSS
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• DECREASED CUTANEOUS BLOOD FLOW.
• DECREASED SWEAT RATE.
• INCREASED CORE TEMPERATURE.
• DECREASED HEAT LOSS AND HEAT TOLERANCE.
• CENTRAL AND/OR PERIPHERAL MECHANISMS MAY BE
  INVOLVED.

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• IN TERMS OF SLEEP LOSS AND LONG-TERM COLD
  EXPOSURE, IT HAS BEEN REPORTED THAT SUSTAINED
  (84-hr) MILITARY OPERATIONS ALTERS
  THERMOREGULATION RESULTING IN GREATER DECLINES IN
  CORE TEMPERATURE DUE TO EITHER A LAG IN THE
  INITIAL SHIVERING RESPONSE OR HEAT REDISTRIBUTION
  SECONDARY TO AN INSULATIVE ACCLIMATION.
• NOTE BOTH SKIN AND CORE TEMPERATURES DECREASE
  IN INSULATIVE ADAPATION RESULTING IN LESS HEAT
  LOST FROM THE BODY TO THE ENVIRONMENT AND MORE
  HEAT TRANSFERRED FROM THE CORE TO THE MUSCLE
  SHELL THEREFORE, THE BODY IS BETTER INSLULATED.

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• HOWEVER, THE DEGREE OF SLEEP LOSS COMMON TO OUR
  SOCIETY DOES NOT APPEAR TO AFFECT WORK OR
  PERFORMANCE MEASURES SUCH AS MAXIMAL OR
  SUBMAXIMAL PHYSICAL WORK CAPACITY.

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OTHER QUESTIONS??