Fluid or hydration status is extremely important in endurance sports like the marathon, getting it wrong can have disastrous consequences. As such hydration is a balancing act, not taking in enough fluids will result in dehydration and taking in too much fluid will result in Exercise-Associated Hyponatremia (EAH). EAH can be a life-threatening scenario where an athlete or individual takes on more fluid than they are losing, causing a dilution and subsequent reduction in sodium levels within the body resulting in fatigue, nausea, vomiting, dizziness and alterations in consciousness.

How Fluid Should Be Replaced

It is uniformly agreed that fluid replacement during exercise is important to prevent excess fluid loss (dehydration) and to avoid body weight loss of >2% and excessive changes in electrolyte balance which can compromise performance. How that fluid is replaced during exercise is currently of great debate with researchers unable to come to a consensus on which approach is best, drinking to a plan of 600-800ml per hour, drinking to thirst (using the sensation of thirst to determine when to drink) or drinking ad libitum (drinking whenever and in whatever volume). In light of this lack of consensus it would seem reasonable that any rehydration strategy should be flexible taking into consideration the duration of the event, the outside temperature, the effort required, sweat rate, the terrain and gradient etc. It should use thirst as a guide while not straying too far from an intake of 600-800ml per hour, but essentially not drinking more than is being lost through sweat.

Sweat Rates

Sweat rates are highly variable between individuals with an average sweat rate of approximately 1.35L/hr. There are calculators available that can help determine ones specific sweat rate. Alternatively, a simple way to establish a rough sweat rate is to weigh one’s self prior to and immediately after a 60 minute workout. The weight loss during that period divided by the time (60mins) will provide a rough sweat rate estimate – it is important to be well hydrated before undertaking the workout. The benefit of establishing an individual sweat rate estimate is it aids in understanding how much fluid is lost to sweat per hour of exercise and therefore roughly how much fluid will need to be replaced per hour.

What To Drink

Armed with a sweat rate estimate and a rehydration strategy of drinking to thirst while making sure one isn’t straying too far from the amount of fluid needing to be replaced due to sweat loss, gives you 2 of 3 key components to a solid hydration strategy. The final component is the fluid type that should to be taken in; water, hypertonic (Gatorade), hypotonic (Mizone) or isotonic (Powerade) drinks. In endurance sports the simple answer to this question is all, it is important to use a mixture of water and drinks that contain electrolytes as well as carbohydrates. Lastly, it is important to try different products and combinations during training to see what works best and to also get used to drinking while training, so when it comes to race day it is one less thing you have to think about.

The Injury Risks From Running

Running season is in full swing at the moment with a plethora of fun runs available, covering 10km, 21 km (half marathon) and 42.2 km (marathon). However, the motivation to run doesn’t necessarily involve competing with others, it could be for stress relief and mental health, general fitness, personal enjoyment or part of a weight loss regime. Regardless of the motivation, injury risks are associated with running where 19% to 79% of runners will experience a running related injury in a given year. Even with improvements in shoe technology helping runners run faster, the injury rates have remained reasonably unchanged since the 1970’s when the modern running shoe was first introduced.

Risk Factors For A Running Injury

Known risk factors related to injury risks in male and female runners include a previous history of an injury, especially in the case of muscle strains and fractures, running with insoles/inserts, and a rapid increase in distance run. There is mixed evidence that absolute high distances (consistently running high distances each week) may or may not be involved with injury risk. Overall, females have a lower injury risk than males however, additional risk factors for women include older age, a longer weekly running distance (48-64km), running on concrete and wearing running shoes for 4-6 months. Whereas males are more at risk if they are restarting running after time away, have been running for less than 2 years and run more than 64km per week. It is also well established that 80% of all running injuries are overuse, this coupled together with the known risk factors for running injuries indicates that training loads play a potential role into why runners experience high injury rates.

Running Load + Injury Risks

What does all of this mean for someone who likes running, it says that although running injuries have multiple causes managing training loads is extremely important to mitigating the risk of injury. With some evidence showing that absolute high training loads can have a protective effect on injury in certain sports, the key is to minimize acute load increases or training spikes. In simple terms this means training loads need to be consistent with small increases in load. A load based model has been put forth called the acute:chronic ratio and it essentially says that the current weeks training load should be between .8-1.3 times the load of the previous 4 weeks of training, if the load is 1.5 times or greater the risk of injury increases.

How To Reduce Your Risk of A Running Related Injury

In lay terms this means if someone is running 5km 2 times per week for 4 weeks and then decides to add a third longer run of 10km a week in the 5th week, they greatly increase their risk of an injury. Does this mean pulling out the calculator to crunch the numbers to get your ratio right, not really. There are plenty of fantastic running training plans available for all levels of runners and all distances, programs that factor in gradual load increases, rest periods and tapering. Running should be enjoyable and injury free regardless of the motivation, so to reduce the risks of sustaining an overuse injury manage the load, gradually increase the kilometres run, avoid training spikes and allow for rest periods. If you do sustain an injury be sure to promptly consult an appropriately trained sports based practitioner/physician.

This research paper looks at quantifying the effects heavier shoes has on running times. Blinded to the runners, the researchers placed lead weights into runners shoes (normal shoe weight, normal shoe weight +100gm and normal shoe weight +300gm) and then had them run on a treadmill and perform a 3km time trial. The data shows that energy costs of the runner increased by 1% for ever extra 100gm of weight.
It should be noted though, there is a lower threshold limit for shoe weight. Ie, having the lightest possible shoe doesn’t mean you will run the fastest. The cushioning of the shoe helps to absorb impact shock and therefore reduces energy expenditure. If you remove too much cushioning, energy expenditure will increase because that cushioning effect is greatly diminished.

Treadmill running with heavier shoes tied to slower race times

The Exercise Is Medicine initiative by the American College of Sports Medicine is continually gaining traction around the world and this article ties into that initiative  exploring the optimum dose of exercise.

Optimum dose of exercise