CESAR CARRERA�EXERCISE & CARDIOVASCULAR DYNAMICS �SPRING 2026

THE INFLUENCE OF THE “NORWEGIAN 4X4” ON CARDIOVASCULAR FUNCTION AND STRUCTURE

THE HEART IS A VITAL ORGAN IN OUR BODY THAT WORKS CONTINUOUSLY TO PUMP BLOOD THROUGHOUT THE BODY AND TO SUPPLY THE PERIPHERAL ORGANS WITH ESSENTIAL ELEMENTS, SUCH AS OXYGEN AND NUTRIENTS. ��THIS WORKLOAD ACCOUNTS FOR APPROXIMATELY 20% OF THE TOTAL OXYGEN CONSUMPTION IN THE BODY AND IS PERFORMED BY THE CARDIAC CONTRACTION SYSTEM TO MAINTAIN MAXIMUM PUMP EFFICIENCY AND CELLULAR METABOLISM¹.

INTRO

EXERCISE TRAINING PROVIDES FAVORABLE ANATOMICAL AND PHYSIOLOGICAL CHANGES THAT REDUCE THE RISK OF HEART DISEASE AND FAILURE.� �AN “ATHLETIC HEART” IS A FORM OF ADAPTATION TO CHRONIC EXERCISE TRAINING IN WHICH CARDIAC REMODELING OCCURS IN RESPONSE TO AN INCREASED WORKLOAD BY UNDERGOING CARDIAC HYPERTROPHY, THE EXPANSION IN SIZE WITHOUT THE PROLIFERATION OF CARDIOMYOCYTES^1.

INTRO

PHYSIOLOGICAL DEMANDS ARE ACCEPTED BY THE CARDIOVASCULAR SYSTEM AS IT ALSO ADAPTS TO THE MORE DOMINANT FORM OF HEMATOLOGICAL STRESS, DEPENDING ON THE TYPE OF EXERCISE.��THE PHYSIOLOGICAL OR MORPHOLOGICAL CHANGES INDUCED IN THE CIRCULATORY SYSTEM MAY DETERMINE THE CATEGORIZATION OF THE TYPES OF EXERCISE¹.

INTRO

RESEARCH HAS SHOWN THAT INTENSIVE CHRONIC AEROBIC EXERCISE LEADS TO CARDIAC MORPHOLOGICAL ADAPTATIONS IN PREVIOUSLY SEDENTARY YOUNG SUBJECTS LIKE THOSE OBSERVED IN ELITE ENDURANCE ATHLETES; HOWEVER, IT IS NOT SUFFICIENT TO ACHIEVE SIMILAR LEVELS OF CARDIAC COMPLIANCE AND PERFORMANCE ².

INTRO

STUDIES HAVE SHOWN THAT EXERCISE INDUCED CARDIAC STRUCTURE AND FUNCTION ADAPTATIONS ARE INFLUENCED BY EXERCISE INTENSITY ^3-4��FOR EXAMPLE, THE MECHANISM WHICH LEFT VENTRICULAR STROKE VOLUME INCREASES DURING UPRIGHT EXERCISE IS DEPENDENT UPON THE CHANGING RELATIONSHIP BETWEEN HEART RATE, LEFT VENTRICULAR FILLING, AND LEFT VENTRICULAR CONTRACTILITY.��AT LOW LEVELS OF EXERTION, AN INCREASE IN LEFT VENTRICULAR FILLING PRESSURE AND END-DIASTOLIC VOLUME ARE IMPORTANT DETERMINANTS OF THE STROKE VOLUME RESPONSE THROUGH THE STARLING MECHANISM. ��AT HIGH LEVELS OF EXERTION, THE EXERCISE TACHYCARDIA IS ACCOMPANIED BY A DECREASE IN END-DIASTOLIC VOLUME DESPITE A PROGRESSIVE INCREASE IN FILLING PRESSURE, SO THAT STROKE VOLUME MUST BE MAINTAINED BY A DECREASE IN END-SYSTOLIC VOLUME ⁵.

INTRO

RESEARCHERS HAVE LOOKED AT HIGH INTENSITY INTERVAL TRAINING (HIIT) TO IMPROVE HEALTH AND INDUCE BENEFICIAL CARDIAC ADAPTATIONS. � �HITT HAS BEEN SHOWN TO:��INDUCE CARDIOVASCULAR BENEFITS IN HYPERTENSIVE MICE ^6��PARTLY REVERSE IMPAIRED AGE-RELATED CARDIAC FUNCTION IN SENIORS^7��IMPROVE CARDIOVASCULAR FITNESS IN ATHLETES IN THE OFF SEASON⁸

INTRO

RESEARCH HAS COMPARED HIIT TO MODERATE INTENSITY CONTINUOUS EXERCISE (MCE) AND FOUND HIIT TO BE MORE EFFICIENT AT INCREASING CERTAIN VARIABLES, WITH PARTICIPATING IN BOTH EXERCISE TYPES REGULARLY SHOWING THE MOST BENEFIT ^9-11.

INTRO

HIIT CAN BE DONE IN A FEW WAYS, WITH 4X4’S AND SPRINT INTERVALS (SIT) BEING THE MOST COMMON. � �RESEARCH HAS FOCUSED MOSTLY ON SIT, WHILE SPARSE DATA HAS BEEN COLLECTED ON 4X4’S .

INTRO

THE PURPOSE OF THIS PROPOSED STUDY IS TO EXAMINE THE INFLUENCE AND SWIFT ADAPTATIONS OF THE NORWEGIAN 4X4 ON CARDIAC STRUCTURE AND FUNCTION.��IT IS HYPOTHESIZED THAT THERE WILL BE CARDIAC STRUCTURE AND FUNCTION CHANGES IN BOTH EXERCISE INTERVENTIONS AT WEEK 6, WITH THE 4X4 SHOWING THE MOST INFLUENCE. ��IT IS HYPOTHESIZED THAT THE 4X4 WILL SHOW MORE CHANGES IN CARDIAC STRUCTURE AND FUNCTION COMPARED TO MCE AT THE END OF THE 12-WEEK PROGRAM. �

PURPOSE&

HYPOTHESIS

METHODS

POPULATION: HEALTHY SEDENTARY ADULTS BETWEEN THE AGES OF 18 AND 30. �WHO MUST BE ABLE TO PERFORM TREADMILL EXERCISE. ��THE INTERVENTIONS WILL BE CONDUCTED 3 TIMES A WEEK FOR 12 WEEKS.�

METHODS

GROUPS - 4X4:��PARTICIPANTS WILL WARM UP ON THE TREADMILL FOR 5 MIN AT 3.0 MPH. ��THE EXERCISE TRIAL WILL CONSIST OF FOUR 4-MIN BOUTS OF TREADMILL WORK PERFORMED AT A HEART RATE (HR) BETWEEN 85 AND 95% OF HR MAX, INTERSPERSED WITH 3 MINUTES OF RECOVERY WORK PERFORMED AT A HR BETWEEN 60 AND 70% OF HR MAX.��A 5-MINUTE COOL DOWN AFTER THE 4 INTERVALS WILL BE USED TO PREVENT ADVERSE EFFECTS.�

METHODS

GROUPS - MCE:��PARTICIPANTS WILL WARM UP ON THE TREADMILL FOR 5 MIN AT 3.0 MPH.��THE EXERCISE TRIAL WILL CONSIST OF 25 MINUTES OF TREADMILL WORK PERFORMED AT A HR BETWEEN 60-70% HR MAX. ��A 5-MINUTE COOL DOWN AFTER THE EXERCISE BOUT WILL BE USED TO PREVENT ADVERSE EFFECTS.�

METHODS

GROUPS - CONTROL:� �PARTICIPANTS WILL SIT IN AN UPRIGHT POSITION FOR 30 MINUTES.

METHODS

VARIABLES

MAX RESTING VALUES FOR:��STROKE VOLUME (SV)�LEFT VENTRICULAR END DIASTOLIC VOLUME (LVEDV)�LEFT VENTRICULAR END SYSTOLIC VOLUME (LVESV)�EJECTION FRACTION (EF)��AS WELL AS CHANGES IN LV WALL THICKNESS AND LV MASS,WILL BE MEASURED USING 3D ECHOCARDIOGRAPHY �

METHODS

RESTING AND EXERCISE CARDIAC OUTPUT (Qc) WILL BE MEASURED USING ACETYLENE REBREATHING AND ANALYZED FOR CHANGES� �PEAK OXYGEN CONSUMPTION (VO₂), HR RESPONSE, AND OXYGEN PULSE WILL BE MEASURED USING CARDIOPULMONARY EXERCISE TESTING (CPET).� �MEASUREMENTS TAKEN AT: �BASELINE, 6-WEEKS, AND POST (12-WEEKS).

METHODS

STATISTICS

LINEAR MIXED-EFFECTS MODEL (GROUP, TIME, AND GROUP X TIME) ��ANALYSIS OF COVARIANCE (ANCOVA; [BASELINE VS POST])

METHODS

ANTICIPATED�FINDINGS

TWELVE PREVIOUSLY SEDENTARY SUBJECTS (AGED 29±6 YEARS; 7 MEN AND 5 WOMEN) TRAINED PROGRESSIVELY AND INTENSIVELY FOR 12 MONTHS SUCH THAT THEY COULD COMPETE IN A MARATHON ².

ANTICIPATED FINDINGS

AVERAGE TRAINING IMPULSE (TRIMP) SCORES PER MONTH FOR ALL SUBJECTS OVER THE TRAINING YEAR. ��BOTTOM DOTTED LINE REPRESENTS THE AVERAGE MONTHLY TRIMP THAT WOULD BE ACCOMPLISHED BY A SUBJECT IN A TYPICAL CARDIAC�REHABILITATION PROGRAM EXERCISING FOR 45 MINUTES AT 75% OF MAXIMUM PREDICTED HEART RATE 3 TIMES PER WEEK;

ANTICIPATED FINDINGS

CHANGES IN LEFT VENTRICULAR (LV) MASS (LEFT) AND RIGHT VENTRICULAR (RV) MASS (RIGHT) MEASURED BY MAGNETIC RESONANCE IMAGING EVERY 3 MONTHS DURING THE 1-YEAR TRAINING PROGRAM. ��MEAN±SD DATA (BARS) ARE SHOWN FOR EACH TIME POINT. NOTE DIFFERENCES IN SCALE FOR EACH GRAPH, WITH LV MASS BEING ≈2.5 TIMES THE RV FREE WALL MASS.

ANTICIPATED FINDINGS

MEAN±SD CHANGES IN LEFT VENTRICULAR END-DIASTOLIC VOLUME (LVEDV; LEFT) AND RIGHT VENTRICULAR END-DIASTOLIC VOLUME (RVEDV; MIDDLE) BY MAGNETIC RESONANCE IMAGING MEASURED EVERY 3 MONTHS DURING THE TRAINING PROGRAM. ��MEAN WALL THICKNESS IS SHOWN ON THE RIGHT TO FACILITATE A VISUAL REPRESENTATION OF THE YEAR-LONG CHANGES IN CARDIAC MORPHOLOGY.

ANTICIPATED FINDINGS

YOUNG AMATEUR ATHLETES IN THE OFF SEASON (7 WEEKS OF SIT).� CHANGES IN LEFT-VENTRICULAR (LV) MASS, LV INTERNAL DIAMETER, POSTERIOR WALL THICKNESS (PWT), AND INTRAVENTRICULAR SEPTUM THICKNESS (IVS) IN RESPONSE TO TRAINING (PRE VS. POST) ⁸.

ANTICIPATED FINDINGS

THIRTEEN MEASURES OF LEFT VENTRICULAR STRUCTURE AND FUNCTION CHANGES SIGNIFICANTLY BY 6 WEEKS OF SIT EXERCISE TRAINING. ���LVEDV, LEFT VENTRICULAR END-DIASTOLIC VOLUME; �LVEF, LEFT VENTRICULAR EJECTION FRACTION; �LVESV, LEFT VENTRICULAR END-SYSTOLIC VOLUME; �LVIDD, DIASTOLIC LEFT VENTRICULAR INNER DIAMETER; �LVSV, LEFT VENTRICULAR STROKE VOLUME.

ANTICIPATED FINDINGS

PERCENT CHANGE IN ABSOLUTE V˙O_2MAX (L·MIN⁻¹) AND ABSOLUTE STROKE VOLUME OF THE HEART (ML·BEAT⁻¹) FROM PRE- TO POSTTRAINING FOR EACH OF THE GROUPS, PRESENTED AS MEAN AND SE. SIGNIFICANTLY DIFFERENT FROM PRE- TO POSTTRAINING: * P < 0.05, ** P < 0.01, *** = P < 0.001.�1)LONG SLOW DISTANCE (70% MAXIMAL HEART RATE; HR_MAX); 2)LACTATE THRESHOLD (85% HR_MAX); 3) 15/15 INTERVAL RUNNING (15 S OF RUNNING AT 90-95% HR_MAX FOLLOWED BY 15 S OF ACTIVE RESTING AT 70% HR_MAX); AND 4) 4 × 4 MIN OF INTERVAL RUNNING (4 MIN OF RUNNING AT 90-95% HR_MAX FOLLOWED BY 3 MIN OF ACTIVE RESTING AT 70%HR_MAX) ¹⁰

ANTICIPATED FINDINGS

4x4 GROUP:�(VS. CONTROL VS. MCE)��EXPECTATION OF GREATER INCREASES IN RESTING MAX VALUES FOR:��SV�LVEDV�EF�LV WALL THICKNESS�LV MASS� �AN INCREASE IN SV WOULD INCREASE RESTING QC��POSSIBLE INCREASE IN LVESV (CHAMBER SIZE)

METHODS

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REFERENCES