Moderate Intensity Continuous Training versus High Intensity Interval Training in Growth Restricted Mice to Improve Cardiac Function: A Pilot Study

Abstract

IntroductionGrowth‐restriction during postnatal development has been linked to increased cardiovascular disease risk in adulthood, with greater impairment seen in females. Growth‐restricted mice present with thinner left ventricle posterior and anterior walls, compromised diastolic function and reduced stroke volume and cardiac output. Regular aerobic exercise training can promote cardiovascular health and well‐being, with recent evidence suggesting high intensity interval training may be more cardio protective as compared to moderate intensity continuous training. The purpose of this investigation was to determine if high intensity interval training (HIIT) promoted cardiac health in postnatally growth‐restricted female mice as compared to traditional moderate intensity continuous training (MICT).MethodsTo induce postnatal growth‐restriction, FVB mouse dams were fed either a 20% protein control diet or an 8% low‐protein isocaloric diet beginning 2 weeks before mating. Only pups born to control‐fed dams were used and cross‐fostered to either a low‐protein fed dam to induce growth‐restriction (PUN) or a different control fed dam (CON). On postnatal (PN) day 21 all pups were weaned and fed a control diet. At PN33 mice were allocated to MICT (PUN n=4, CON n=3), HIIT (PUN n= 4, CON n= 3) or a corresponding sedentary group (MICT: sedentary PUN n= 5, sedentary CON n=4; or HIIT: sedentary PUN n= 5, sedentary CON n=4). The MICT protocol was defined as treadmill running 3 days/week for 12 weeks at 17 m/min at −16 degree decline for 28 minutes and the HIIT protocol was treadmill running 5 days/week for 8 weeks with alternating intervals of 8 mins at 85% and 2 mins at 55% of maximum workload for 60 minutes. At PN 128 (MICT) and PN 98 (HIIT) echocardiography and Doppler blood flow was utilized to measure cardiac structure and function under 1% isoflurane anesthesia. Statistical analysis was performed using GraphPad Prism 8, utilizing two‐way ANOVAs with an alpha level of .05 set a priori and if significant Tukey’s post hoc for multiple comparisons was conducted.ResultsSedentary PUN groups exhibited cardiac dysfunction as evident by reduced left ventricle (LV) area during systole (p=.0290), LV diameter during diastole (p=.0156) and systole (p=.0003) and LV volume during systole (p=.0191). Systolic function was compromised in the PUN sedentary group by impaired myocardial performance index (MPI) (p=.0049), ejection fraction (EF) (p=.0023), aortic ejection time (AET) (p=.0345) and fractional shortening (FS) (p=.0111). Diastolic impairment manifested as reductions in isovolumic relaxation time (IVRT) (p=.0102) and mitral valve deceleration time (MVDT) (p=<.0001) in the PUN sedentary group. Both MICT and HIIT were able to reverse impairments as no significant differences were noted between exercised PUN groups and their CON counterparts.ConclusionMICT and HIIT both reversed the cardiac impairments caused by growth‐restriction. Impairments caused by growth‐restriction can be mitigated with exercise training. Importantly, exercise professionals have flexibility in prescribing exercise as both MICT and HIIT were shown to be effective.