Methods
Full details of the protocol have been previously published8 and this was a pre-planned ancillary analysis.
Healthy participants were recruited in 2016 prior to undertaking
training their first marathon (Virgin Money London). Inclusion criteria
age was less than 35 years at recruitment, no past significant medical
history and no previous marathon running experience. All procedures were
in accordance with the principles of the Helsinki declaration. All
participants gave written informed consent and the study was approved by
the London-Queen Square National Research Ethics Service Committee
(15/LO/0086).
All measurements were conducted before training started over a
three-week period (three consecutive weekends after ballot place
announcement), six months prior to the marathon.
Data acquisition and
analysis
Cardiopulmonary exercise testing (CPET) was performed according to
exercise testing guidelines 9. Protocols were
individually determined with work rate (15-30 W) increased every minute
until voluntary exhaustion, aiming for 10 minutes of exercise. To permit
concurrent transthoracic echocardiography, studies were performed using
a semi-recumbent cycle ergometer (ERG 911 S/L, Schiller, Baar,
Switzerland). A 1-minute rest period was included followed by a 3-minute
warm up. Heart rate (HR), blood pressure and oxygen saturation were
monitored throughout. VO2 was continuously measured
using a calibrated breath-by-breath analyser (Cosmed Quark CPET, Rome,
Italy). Participants were verbally encouraged to exercise until maximal
exertion. VO2peak was expressed as the highest value
from an average of 30 seconds during the final stage of the exercise
test. To fully assess submaximal efforts, the oxygen uptake efficiency
slopes (OUES) was calculated automatically from VO2against the logarithm of VE (logVE)10.
Echocardiography was performed using a GE Vivid E95 platform
(Vingmed-General Electric, Horten, Norway) equipped with a phased-array
transducer (1.4-4.6 MHz). A detailed protocol was collected at rest, at
5 minutes into exercise (excluding the 3-minute warm-up period), and
when the respiratory exchange ratio (RER) was above 1.0. This included
the apical 4-chamber view (with and without tissue velocity imaging
(TVI), the apical two-chamber, apical long axis view, parasternal short
axis view at the base and apical level, and a PW at the level of the
Left ventricular outflow tract (LVOT) (one centimetre below the aortic
valve). An abbreviated protocol was obtained every 1 minute and 15
seconds and included the apical 4-chamber view (with and without TVI).
As part of the protocol 12-lead ECG and cardiac magnetic resonance was
undertaken but not included in this analysis.