With a Year of Endurance Training, the Sedentary Can Have an Olympian's Big Heart

October 14, 2014

DALLAS, TX — With less than a year of high-level endurance training, ordinary Joes can achieve the kind of left and right ventricular structural changes seen in elite, Olympic-level athletes, but probably without the boost in cardiac compliance and performance that comes from years of dedication to exercise, according to researchers[1].

They came to that conclusion after using echocardiography, cardiac MRI, and other tests to follow 12 initially sedentary adults who engaged in a yearlong endurance training program to prepare for running a marathon or similarly challenging sports event. By month 12, the participants' right and left ventricles had grown in mass and volume in proportion to each other, but interestingly, the two chambers got there at different rates.

During the training program, which intensified over the months, their RV mass and volume went up progressively and consistently. That process of "eccentric" remodeling started right away; the changes were evident at the first comprehensive follow-up at three months, the group reported in a paper published October 3, 2014 in Circulation, with lead author Dr Armin Arbab-Zadeh (Texas Health Presbyterian Hospital, Dallas).

On the other side of the heart, on average, LV mass responded to training by growing in mass but not volume for the first six months, a process of "concentric" remodeling. But thereafter the pattern started to shift.

"It wasn't until we had longer sessions or high-intensity sessions that the left ventricle started to dilate, and eventually it did," Dr Benjamin D Levine (University of Texas Southwestern Medical Center, Dallas) told heartwire . "Toward the end of the program we generated the same phenotype, eccentric hypertrophy of both ventricles, that you see in endurance athletes."

Levine said he was "quite surprised and intrigued" that the right ventricle begins the proportional mass-volume growth of eccentric remodeling right away. "Even a walking program will start that process. The left ventricle? You've got to work it a little bit harder before it starts to dilate, even though once you increase its work, it starts to build muscle mass."

Those observations may suggest that the immediate RV mass and volume adaptations to intense exercise—in contrast to the mass-only changes seen at this time point in the LV—allow the left ventricle to fully adapt in structure and function. "The right ventricle feeds the left ventricle," he noted. "One might speculate that the right ventricular adaptation is permissive, that you have to have that adaptation first so the right ventricle can keep up" with the left ventricle.

On average for the left side of the heart, the group reported:

  • Mean LV wall thickness and LV mass climbed in the first six months and rose less sharply thereafter.

  • LV end-diastolic volume (LVEDV) remained essentially unchanged the first three months, had risen by only 8% after six months, and (after initiation of the interval training phase of the exercise program) climbed more steeply thereafter.

  • The LV mass-to-volume ratio increased from 1.44 at baseline to 1.58 at both three and six months (concentric hypertrophy), "and then returned to values close to baseline [eccentric hypertrophy] after nine and 12 months of training."

On the right side of the heart:

  • Mean RV free-wall mass went up 30% and RV volume rose 27%, more sharply than either measure in the left ventricle: 22% and 20%, respectively.

  • RV mass and volume rose together in a pattern of eccentric hypertrophy throughout the 12 months, spanning all levels of training; the mass-volume ratio started at 0.46 and had risen to only 0.47 (not significant) by the end of training.

Left, Right Ventricular Mass, and Diastolic, Stroke Volumes* Over 12 Months of Endurance Training

Parameter Baseline Month 3 Month 6 Month 9 Month 12
LV Mass (g) 168 188 198 199 203
LVEDV (mL) 117 119 125 136 138
LVSV (mL) 79 85 89 97 98
RV Mass (g) 63 71 72 75 82
RVEDV (mL) 136 156 161 172 173
RVSV (mL) 78 87 90 97 97
*By cardiac MRI
LV=left ventricular
RV=right ventricular
EDV=end-diastolic volume
SV=stroke volume

VO2max increased significantly from 40.3 mL/kg/min at baseline to 48.7 mL/kg/min after one year, along with rises in both cardiac output and stroke volume.

Exploration of pressure-volume relationships showed that "for any given filling pressure, LVEDV was greater after training compared with baseline (P=0.0001), consistent with increased ventricular distensibility and/or reduction of pericardial constraint."

However, "even though we generated the same training stimulus and we got the same left ventricular mass [adaptations], we didn't get anywhere near the same compliance and flexibility and size of [the heart in] the elite athlete," according to Levine.

"It may just be that they didn't train long enough, that's possible," he said. Or, he speculates, because Olympic athletes usually start training when they're very young, often before a growth spurt in adolescence, perhaps they can achieve greater myocardial growth and compliance than older people training to a similar degree. Also, training during youth may allow the pericardium to grow proportionally more than with training in adulthood, by which time the pericardium is stiffer, which may lessen the impact of pericardial restraint in adulthood.

All subjects successfully completed the event that was their goal for training, the group writes: a marathon for 10 of them, an "Olympic-distance triathlon" for one, and a 100-mile endurance cycling race for one.

Arbab-Zadeh, Levine, and the other authors have reported no relevant financial relationships.


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