EFFECTS OF GENDER,
AGE, CIRCADIAN
RHYTHMS, AND SLEEP
LOSS ON THERMAL
RESPONSES DURING
EXERCISE
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.
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.
GENDER DIFFERENCES IN
THERMOREGULATION
GENDER DIFFERENCES
RELATED TO THE
MENSTRUAL CYCLE
• 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.
• INCREASED
ESTROGEN
STIMULATES:
• PROLIFERATION
OF UTERUS
ENDOMETRIUM
(MUCOUS
MEMBRANCE OF
UTERUS).
• INCREASED
ESTROGEN
STIMULATES:
• SECRETION OF LHRF
FROM
HYPOTHALAMUS,
WHICH STIMULATES
INCREASED RELEASE
OF LH AND FSH (13TH15TH 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).
• 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.
• IF FERTILIZATION DOES
NOT OCCUR, THE
CORPUS LUTEUM
DEGENERATES
RESULTING IN
DECREASED
PROGESTERONE
SECRETION, WHICH
LEADS TO
ENDOMETRIUM
DEGENERATION AND
MENES BEGINS.
• 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.
• 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.
• NOTE: PARALLEL CHANGES IN
SUDOMOTOR (SWEATING) AND
VASOMOTOR (VASODILATION)
RESPONSES INDICATES THAT
THERE IS A CENTRAL ALTERATION
IN THERMOREGULATORY CONTROL
WITHIN THE HYPOTHALAMUS.
•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.
WORK-HEAT TOLERANCE
• 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.
• 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.
• 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.
GENDER DIFFERENCES
• 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.
• 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.
CARDIORESPIRATORY
FITNESS LEVEL
(I.E., MAXIMAL OXYGEN
UPTAKE RATE)
AND HEAT TOLERANCE
• 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.
AGE AND HEAT TOLERANCE
AGE AND HEAT TOLERANCE
OLDER ADULTS - LOWER
HEAT TOLERANCE
• 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.
• 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 (??).
• DECREASED SWEATING CAPACITY
DUE TO A DECREASE IN TOTAL BODY
WATER.
• DECREASED CONVECTIVE,
EVAPORATIVE, AND RADIANT HEAT
LOSS.
• REDUCED ABILITY TO ADAPT TO
HEAT.
YOUTH - LOWER HEAT
TOLERANCE
• 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.
• HIGHER PERCENT BODY FAT.
• HIGHER THRESHOLD FOR ONSET OF
SWEATING (??).
• SWEATING SENSITIVITY (??).
• POSSIBLY A DECREASED CAPACITY
FOR SWEATING DUE LOWER TOTAL
BODY WATER.
• 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.
• 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.
• 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.
CIRCADIAN RHYTHMS
ZEITGEBERS
• EXTERNAL RHYTHMIC INFLUENCES
THAT PROVIDE TIME CUES, WHICH
SYNCHRONIZE CIRCADIAN
RHYTHMS WITHIN AN INDIVIDUAL.
• NORMAL SYSTEMS OSCILLATE IN A
24 HOUR CYCLE.
ZEITGEBERS
• WITHOUT ZEITGEBERS, CIRCADIAN
RHYTHMS BECOME FREE RUNNING:
-
CORE TEMPERATURE FOLLOWS 25
HOUR CYCLE.
-
SLEEP/WAKE 25 HOUR CYCLE.
EXAMPLES OF EXTERNAL
RHYTHMIC INFLUENCES
• LIGHT/DARK CYCLE.
• SLEEP/WAKEFULNESS CYCLE.
• SOCIAL ACTIVITY.
• FEEDING/FASTING CYCLE.
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.
EFFECTS ON
THERMOREGULATION
• 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.
• 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.
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.
• Among all intra-time zone rivals,
home teams won 56% and away
teams won 44% on the games
between 1978-1987 in the NFL.
• 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.
• 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.
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.
SLEEP LOSS
TYPES OF SLEEP
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.
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.
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.
REM SLEEP IS ASSOCIATED WITH:
• RESTORATIVE PROCESS.
• IRREGULAR HEART RATE AND
RESPIRATORY RATE.
• SOME IRREGULAR MUSCLE MOVEMENT
SUCH AS RAPID EYE MOVEMENT (REM).
REM SLEEP IS ASSOCIATED WITH:
• ACTIVE BRAIN PATTERNS.
• MAY ENHANCE THE
CONSOLIDATION OF LONG-TERM
MEMORY.
• 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.
SLEEP LOSS
• DECREASED CUTANEOUS BLOOD FLOW.
• DECREASED SWEAT RATE.
• INCREASED CORE TEMPERATURE.
•
DECREASED HEAT LOSS AND HEAT
TOLERANCE.
•
CENTRAL AND/OR PERIPHERAL
MECHANISMS MAY BE INVOLVED.
• 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.
• 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.
OTHER QUESTIONS??