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 (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).

• 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 ADAPTTO 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 FORHEAT 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, ANDRADIANT 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??