Consider Your Calories
Although estimates vary, studies show that there can be up to a twofold increase in calorie burn during cold-weather exercise, particularly during strenuous training sessions in wet or icy conditions.
Not only does the weather provide additional resistance (think rain, snow and sleet), the weight of additional clothing, thermoregulation and inefficiency of cycling in cold weather can all increase calorie burn.
Cold weather cycling may also blunt appetite, and a failure to consume sufficient calories, protein or carbohydrate can significantly impair performance, recovery and immunity. At the other end of the scale, if you find that your training volume and intensity has reduced, you may need to reduce your calorie intake to maintain your weight.
Be aware of changes to your training sessions and adapt according. The easiest way to assess whether you're achieving the right energy balance is to keep an eye on the scales - a pound of body weight is roughly equivalent to 3,500 calories, so to gain (or lose) a pound a week, you're looking at an increase (or deficit) of around 500 calories a day.
Whether you're training for fun or competition, experts agree that maintaining an adequate fluid intake is one of the biggest challenges presented by cold- weather workouts.
Unlike in warm temperatures when physiological mechanisms prompt us to drink, feelings of thirst are blunted in the cold, despite sweat loss. And as recognising thirst becomes more difficult, the risk of dehydration increases.
In one study comparing the hydration levels of athletes performing cold or warm weather sports, the cold-weather team had the highest incidence of dehydration, with voluntary fluid intake insufficient to meet the demands of exercise.
More recently, in a study commissioned by the International Olympic Committee, researchers found that voluntary fluid intake and drive to drink were significantly lower in winter sport athletes, blamed on the belief that sweat loss during cold-weather workouts was insignificant.
But it's not just a reduction in drive to drink that's to blame: exercising in cold conditions increases water loss via respiration, as the body is forced to warm and humidify the cold dry air breathed in.
In addition, the constriction of blood vessels in cold weather causes an increase in the fluid circulating the body's core organs, which the body tries to restore by increasing urine output, a phenomenon known as ‘cold diuresis'.
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Bottom line - although sweat losses tend to be lower in winter, you're still at risk of dehydration due to reduced fluid intake and water loss via respiration and increased urination. And since even mild dehydration can affect performance, maintaining an adequate intake of fluid during cold weather rides should be a key priority of any training plan.
Aim to start your training sessions well hydrated, start drinking early on in your ride, and adopt regular drink ‘breaks' every 15-20 minutes.
Weighing yourself before and after a typical session wearing minimal clothing will help you determine whether you are consuming adequate fluids - remember you're aiming to minimise loss of body weight to less than two per cent. Although less precise, monitoring your urine colour and volume is a helpful indicator - if you're well hydrated it will be plentiful and straw coloured.
Warm fluids may be tolerated more readily when exercising in the cold, and can increase your motivation to drink - try an insulated container or wrap your sports bottle in clothing or a sock to prevent it becoming too cold. You should also be able to open any drink bottle with your gloves on.
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All hail carbohydrates
As the body's preferred source of energy, carbohydrates are king when it comes to fuelling endurance exercise, although the body's limited capacity for storage necessitates a regular intake to delay fatigue.
This becomes particularly important during cold weather, as shivering accelerates the use of muscle and liver glycogen (stored carbohydrate). In studies dating back to the early Nineties, scientists studying groups of men made to shiver for two hours discovered a sevenfold increase in carbohydrate oxidation, compared to less than a twofold increase in fat oxidation.
More recently, research has demonstrated that while rates of fat and protein oxidation remain relatively constant during exposure to cold, carbohydrate oxidation is stimulated, with studies suggesting the dominant source being muscle glycogen, particularly as shivering intensifies, or when plasma glucose levels are low.
Couple this with the carbohydrate demands of longer rides, and the risk of glycogen depletion increases, which can lead to dips in performance and early fatigue, increasing the risk of injury, particularly on icy terrain.
But it's not just early fatigue - glycogen depletion can also impair thermoregulation, resulting in more rapid decline in body temperature.
Interestingly, research suggests that an early (rather than delayed) intake of glucose during cold exposure can reduce reliance on the body's glycogen stores, delaying time to exhaustion. To avoid early fatigue, plan accordingly.
A meal containing slow- release carbohydrates eaten two to three hours prior to a bike session will top up glycogen stores and extend carbohydrate availability - try a bowl of hot porridge oats topped with baked fruit, eggs on toast, soup and bread, a baked potato, or a banana and peanut butter sandwich.
Failing that, a small carbohydrate-rich snack such as raisins or a banana eaten 30-60 minutes prior to exercise will boost blood glucose levels. Refuelling during rides of up to 60 minutes isn't necessary if your habitual diet and pre-ride meals contain sufficient carbohydrate.
For rides lasting over an hour, 30-60g of carbohydrates per hour is recommended to maintain blood glucose levels - isotonic sports drinks or sports gels are convenient, although a recent study from Appalachian State University demonstrated that bananas were as effective as sports drinks in fuelling endurance rides (a medium banana contains around 30g of carbohydrate).
As with fluids, any ‘on bike' fuel should be easy to open and eat without needing to remove gloves. Easily consumed sources of carbohydrates include bananas, fig rolls, trail mix, oat and fruit based energy bars, sports drinks, gels, jam or honey and banana sandwiches.
Remember that if you're opting for a gel or solid food over a sports drink you'll need to factor in fluid intake too.
Post-workout, a meal or snack containing a mix of carbohydrate and protein will optimise glycogen resynthesis and aid muscle recovery - if you're aiming to cycle again within eight hours, aim to start re-fuelling within 30 minutes of leaving the bike.
Recovery options include a pint of milk and a banana, a bowl of cereal and milk, a bagel with soft cheese and soup, chicken stir-fry with noodles or a sandwich with a protein filling.
Warm it up
Consuming cold foods and fluids in chilly weather doesn't just reduce your motivation to eat and drink - they can also contribute to a dip in body temperature.
From a practical standpoint, icy drinks and semi-frozen sports bars or snacks are also difficult to eat (not to mention unpalatable), which can lead to dehydration and fatigue if you're unable to consume sufficient amounts during your ride.
To avoid this, opt for warm foods and fluids before, during and after training using insulated containers if needed. Sports drinks can be warmed for sessions on the bike, and a thermos of hot chocolate is a comforting recovery option - studies show chocolate milk to be an effective recovery aid, thanks to the combination of protein and carbohydrates.
When it comes to post-workout meals, hot healthy dishes such as oatmeal with milk, hearty soups with chunky bread, chilli and rice, meatballs and pasta, or winter stews with baked potatoes will aid the recovery process. Desserts such as rice pudding or baked fruit and custard also provide a good mix of protein and carbohydrate.
Bolster your immunity
Flu season takes hold in the winter, and this, coupled with the immune-dampening impact of intense training, can significantly increase the risk of illness and interruptions to training.
Research also shows rates of upper respiratory tract infections (affecting nose, mouth, and bronchial passages) are increased during winter months due to the fact that cold, dry air favours the survival and transmission of viruses.
Aside from adopting a policy of regular hand-washing to avoid the spread of germs, a well-balanced and nutritious diet is your best bet for bolstering immunity. Include plenty of brightly coloured antioxidant-rich fruit and vegetables, lots of essential fatty acids (fatty fish, walnuts and omega 3-rich eggs) and immune boosting ingredients such as coconut oil, fresh garlic, chilli and ginger.
A healthy balance of gut bacteria is also vital to immune function, with research showing that a daily probiotic can boost immunity by reinforcing the gut barrier.
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In a 2011 study led by scientists at Loughborough University, a daily probiotic supplement taken during four months of endurance-based winter training was effective in reducing the incidence of respiratory infections in a group of highly active men and women.
If you don't want to splash out on a probiotic, consume a daily serving of live yoghurt - the natural active cultures can stimulate immune function, with some research suggesting regular intake is as effective as probiotic supplementation.
Another supplement worth considering is vitamin D - as the majority of our stores are made via the action of sunlight on the skin, deficiency is common during winter months, with low levels linked to a greater risk of colds and flu. As dietary sources are limited to fatty fish, eggs and butter, a supplement can act as a safeguard, particularly if your sunlight exposure has been limited in the earlier months.
And although it won't prevent you becoming ill, experts believe a mega dose of vitamin C can help reduce the length and severity of symptoms if you do develop a cold - up to 1,000mg is thought to be effective.
Foods highest in vitamin C include peppers, dark green leafy veg, kiwis and oranges.
Remember that a lack of sleep and high stress levels can also influence immune function, so aim to establish a good sleep habit by going to bed at the same time each evening, turning off electronic devices and avoiding alcohol.
Think ahead: Plan, Prepare, Perform
To fuel effectively for winter rides you need to think ahead and prepare accordingly - leave it to chance and you could find yourself with just a semi-frozen sports drink for company.
Consider the length of your rides, any pit stops you might have, and the availability of foods and fluids when you get to the end. It's also wise to think about whether there is somewhere you can heat food up, or whether you need to take a thermos or insulated drinks bottle with you.
To save time, cook hot foods in bulk - soups and stews can be prepared at the beginning of the week and individually portioned ready for pre or post-ride nutrition - serve with crusty bread, rice, noodles and fresh vegetables.
Make sure food and fluids are available for the recovery period, whether that's at work, at home, or elsewhere. If convenience or heating foods is an issue, it might be an idea to keep a stash of instant soup, hot chocolate or oat sachets in your kit bag.
Last but not least, remember that icy conditions are hazardous, which means you should carry some emergency rations in case of any events which leave you out in the cold for longer than anticipated - dried fruit, chocolate, raisins and peanuts, a Snickers or energy bar are popular choices.
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