Inorganic Nitrate: Sex Differences in Muscle Contractile Function and Efficiency
Inorganic Nitrate: Sex Differences in Muscle Contractile Function and Efficiency
Dietary inorganic nitrate, in the form of beet root juice, is a nutritional intervention, considered to be an exercise enhancer due to its capacity to increase Nitric Oxide (NO) bioavailability. Increasing NO bioavailability has been associated with improved mitochondrial respiration, muscle tissue perfusion and contractile function which may lead to improved exercise capacity. However, the majority of the literature is on male subjects. This limits the applicability of this supplement in females. Therefore, our project aims to determine sex-differences and the specific sex-response across the menstrual cycle of dietary nitrate supplementation on exercise efficiency, strength and fatigue resistance.
Dietary inorganic nitrate is a nutritional intervention, considered to be an exercise enhancer due to its capacity to increase Nitric Oxide (NO) bioavailability. Increasing NO bioavailability has been associated with improved mitochondrial respiration, muscle tissue perfusion and contractile function which may lead to improved exercise capacity. The amount of research investigating the effects of beet root juice supplementation (which contains a high concentration of inorganic nitrate) on exercise responses has increased dramatically in the last 10 years-with over 150 studies in the literature. To date there are only 7 studies looking at exercise responses following inorganic nitrate supplementation specifically in females. Given the physiological differences between males and females studies looking into sex-differences and the specific sex-response are warranted.
The purpose of this study is to investigate whether dietary nitrate supplementation has different effects on muscle contractile function in males and females. We will assess muscle function during an isokinetic protocol where subjects will have to produce maximum efforts at three different torque development speeds (i.e. 180, 270 and 360). This will be followed with a fatigue protocol which will consist of intermittent voluntary contractions at 60% of their maximal voluntary contraction until exhaustion provided by research in the Sport Medicine - Kinesiology department. Thus, we will be able to distinguish the effect of dietary nitrate on contractile function and its capacity to delay fatigue in a sex-specific manner.
The hypothesis of this study is that there will be a group difference between males and females for change in peak power and time to exhaustion after consuming dietary nitrate (in the form of concentrated beetroot juice) for 5 days.
In order to test this hypothesis, we will recruit 24 healthy recreationally active individuals (12 females + 12 males) in a randomized, double-blind, placebo controlled, cross over design.
Specific Aim 1: Determine the sex-differences of the effect of dietary nitrate supplementation on peak power. We hypothesize that the males will have larger improvement in peak power following dietary nitrate.
Specific Aim 2: Determine the sex-differences of the effect of dietary nitrate on fatigue during an intermittent isometric fatigue protocol. We hypothesize that the females will have a greater improvement in fatigue resistance than males.
Specific Aim 3: Determine the sex-differences of the effect of dietary nitrate on oxygen consumption during sub maximal exercise.
Inclusion Criteria:
Male and female participants in good general health as assessed by the standard procedures described below and specifically meeting normal blood pressure range (systolic: 120-129, diastolic: 80-84) and normal BMI range (18.5-24.9)
Exclusion Criteria:
• Known pulmonary, cardiovascular or metabolic disease