Flashcards in Example SAQs Deck (6)
Explain the mechanisms by which sodium bicarbonate
improves exercise performance.
Acidosis can impair muscle function and be involved in muscle fatigue development. buffering agents such as sodium bicarbonate may enhance high intensity exercise performance where there is significant H+ ion accumulation.
Alkalising agents such as sodium bicarbonate may reduce the accumulation of extracellular potassium ions which is also an important factor in fatigue.
Sodium bicarbonate supplementation at a dose of 0.3g.kg-1 60-90 min pre-exercise is optimal, but care is required due to the risk of GI distress and nausea. This results in increased plasma and red blood cell bicarbonate ion concentration, this increases H+ efflux from the muscle so preserving pH. H+ reacts with bicarbonate to form carbonic acid which then dissociates to water and carbon dioxide and the latter is then expired resulting in an RER > 1.
Describe the physiological roles of Vitamin D, and discuss the rationale for Vitamin D supplementation for athletes particularly those competing in indoor events
The physiological roles of vitamin D include supporting bone health, muscle function and immune function. Specifically vitamin D:
• Increases phosphate and calcium absorption and there is evidence that bone mineral density is positively associated with vitamin D status
• May be involved in calcium kinetics and poor vitamin D status is associated with muscle weakness
• May support macrophage and monocyte function there is evidence of increased upper respiratory tract infection rate with poor vitamin D status.
There is evidence that there is a high prevalence of Vitamin D insufficiency and even deficiency during the winter months in particular and for athletes competing in indoor events (Halliday et al, 2011). Since poor vitamin D status is associated with muscle weakness as well as poor bone health and immune function, there is a clear rationale to improve vitamin D status in deficient athletes. The suggested dose is 4000 IU per day and this has been shown to be effective at restoring vitamin D status to recommended levels (>50 nmol.l-1 25(OH)D concentration) over a 6-12 week supplementation period in athlete populations (Close et al, 2013). However, there is little direct evidence to suggest that this results in improved exercise performance, unless athletes were vitamin D deficient (<30 nmol.l-1 25(OH)D concentration) (Close et al, 2013).
A body builder is attempting to maximise muscle mass
gains, what protein feeding strategy would you
recommend and why. Ensure that you consider type,
amount and timing of feeding
Whey protein is rapidly absorbed and leucine enriched and is therefore the most effective post-exercise protein supplement. Consuming 20g (~0.24g.kg-1) immediately (Moore et al, 2015) and every 3h during recovery from exercise has been shown to maximise rates of myofibrillar protein synthesis (Areta et al, 2013). In addition consuming protein prior to sleep has also been shown to support higher rates of muscle protein synthesis during the overnight period (Res et al, 2012). Athletes should not exceed a total protein intake of 1.7 g.kg-1.d-1, and for body builders who want to minimise fat mass it is important to achieve avoid excess energy intake.
Muscle glycogen depletion is a key cause of fatigue during endurance exercise, what carbohydrate feeding strategy would you recommend to maximise recovery and what mechanisms are involved.
Speedy refuelling would take the form of 1-1.2g/kg/h for the first 6h of recovery with 10-12g/kg consumed over the first 24h of recovery. This would be important if you were looking to perform exercise either again that day or had multiple competitions on consecutive days. Glycogen synthase is the enzyme which is responsible for the rate-limiting step of glycogen synthesis and is present in two forms. The active form of this enzyme is increased by insulin. Therefore insulin acts to increase glycogen synthesis. In addition insulin induces Glut 4 translocation to the sarcolemma to allow glucose uptake into the muscle, which provides the substrate for glycogen synthesis. Studies have investigated whether alterations to insulin response results in greater glycogen synthesis. Protein has been shown to increase the insulin response, however when there is sufficient carbohydrate ingested there is no additional effect of protein on glycogen resynthesis (review see Betts 2010). The story is similar with single amino acid ingestion of glutamine too (Bowtell, 1999). Another suggestion to increase muscle glycogen synthesis is coingestion of caffeine. However, similarly to protein the effect of caffeine is only present if there is insufficient carbohydrate ingested.
What is the recommended daily intake of protein for endurance athletes? Describe the possible benefits associated with whey protein supplementation for endurance athletes.
A nitrogen balance study by Meredith et al (1989) found that the RDI for protein for endurance athletes is 1.26g.kg-1.d-1 but most endurance athletes consume in excess of this amount. Dietary protein intake can be more marginal for female endurance athletes especially if they are consuming a hypocaloric diet.
Protein supplementation after endurance exercise results in greater rates of myofibrillar protein synthesis (Breen et al, 2011), and may therefore help to improve recovery from exercise.
When consuming a hypocaloric diet, increased dietary protein intake helps to conserve the muscle mass (Mettler et al, 2010).
Protein ingestion during endurance exercise does not seem to improve performance when adequate carbohydrate is consumed.