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Welcome to the HPRC Blog. We've got lots of information here, from quick tips to in-depth posts about detailed human performance optimization topics.

HPRC Fitness Arena: Environment

Compression garments: Do they work?

Compression socks, sleeves, and other garments are popular among athletes, but do they actually increase performance and decrease recovery times?

Compression garments come in a variety of sleeves, socks, shorts, and full-body suits. The amount of pressure, or compression, they provide depends on the type and size of the garment. Compression garments help push blood toward your heart and prevent it from “pooling” or collecting in the compressed areas. Compression sleeves also are used in clinical settings for those with lymphedema, where blood circulation is poor, or to prevent blood clots.

But can they increase your performance and decrease your recovery times? Compression garments have been shown to help blood flow to working muscles during exercise, but that necessarily doesn’t translate to better performance. Most studies look at compression socks during running, and most evidence suggests no difference in athletes’ performance levels during runs when compared to those not wearing compression socks. In addition, there’s no decrease in recovery time or blood-lactate levels.

Still, those wearing compression socks report “feeling better” and “less tiredness” in their legs during their runs. They also feel less sore following the exercise bout. And while there might not be an actual benefit of wearing compression gear, if you feel better wearing it—either during or after exercise—then keep doing what works!

Swimmers: Don’t hold your breath

HPRC Fitness Arena: Environment, Total Force Fitness
What is hypoxic blackout and how can you prevent it?

Swimmers and free divers who hyperventilate before holding their breath for long periods underwater are at risk of hypoxic blackout—loss of consciousness—that can result in brain damage and death. (It sometimes is known as “shallow water blackout,” but this can be confusing because there are other causes of “shallow water blackout.”)

Hypoxic blackout often affects skilled, fit, and competitive swimmers and free divers. They practice breath holding or hypoxic training in water to increase their ability to hold their breath for longer periods of time. But depending on the technique, this can be a dangerous practice.

Breathing is a process of exhaling carbon dioxide (CO2) and inhaling oxygen. The actual urge to breathe is caused by a buildup of CO2 within your lungs. If you simply try to hold your breath underwater, the physiological urge to breathe will eventually take over so there isn’t a significant risk of “passing out.” However, some swimmers and free divers have found that if they hyperventilate before diving into the water —either by rapid breathing or taking deeper breaths—they can hold their breath for longer periods of time. It’s the act of hyperventilating that can be deadly.

When you hyperventilate before underwater swimming, the amount of CO2 is reduced in your lungs and the urge to breathe is diminished. Without warning, you can lose consciousness—at which point a breath is forced and water fills your lungs. Unless rescue is immediate, brain damage and death are likely outcomes.

Training with instructors and a skilled free-dive or swimming community will help reduce your risk of tragic accidents. In addition, there are other things you can do to avoid hypoxic blackouts.

  • Don’t hyperventilate before underwater swimming.
  • Never swim alone.
  • Don’t ignore the urge to breathe underwater. 

Prevent altitude sickness

HPRC Fitness Arena: Environment, Total Force Fitness
Altitude sickness can affect your performance. Learn about what happens to your body and how to look for warning signs.

Altitude affects what your body needs and how it responds, especially when it comes to exercise. Acute mountain sickness (AMS)—caused by dry air, a decrease in oxygen, and low barometric pressure—can severely impact your health and performance. The good news is there are things you can do to help reduce your risk of altitude sickness.

Performing physical activity—whether you’re at the gym or on a mission—at moderate (4,000–7,900 ft or 1,200–2,400 m) and high (7,900–13,000 ft or 2,400–4,000 m) altitudes can be challenging. At high altitude, oxygen pressure is significantly lower, which results in less oxygen in the blood and muscle tissues. And as altitude increases, there’s also a decrease in air temperature (about 2°F for every 500 ft or 150 m), less moisture (resulting in drier air), and increased solar radiation. AMS can affect anyone who is unacclimatized and ascends too rapidly to high altitudes. Symptoms can include headache, nausea, fatigue, dizziness, vomiting, sleep problems, shortness of breath, dehydration, and impaired cognition and balance.

The risk and severity of altitude sickness are greater above 4,000 meters, and treatment might require evacuation to lower altitude or immediate medical attention. To reduce your risk of AMS, wear sunscreen, drink water, and try to limit your physical activity at altitude for the first 24 hours. Acclimate to moderate elevations (2,000–3,000 m), if possible.

With current and future military operations in mountainous regions, the issue of AMS is a serious concern. However, leaders can help manage and perhaps prevent AMS among Warfighters by being aware of the elevation, types of activities, and lengths of stay at altitudes. Visit HPRC’s Altitude section to learn more about performance at altitude.

Expired sunscreen: Is it safe?

HPRC Fitness Arena: Environment, Total Force Fitness
Check the expiration date on your bottle of sunscreen before heading outdoors for summer fun.

Take note: Your sunscreen—important for protecting your skin from the sun’s harmful ultraviolet rays—has an expiration date! Just as you wouldn’t expect to feel well after eating expired food, don’t rely on expired sunscreen to protect you from the sun.

Sunscreen can be effective for up to 3 years. After that, its active ingredients start to deteriorate, leaving you vulnerable to sunburn and sun damage. Ideally, you should use sunscreen often enough that your bottle doesn’t last through the summer. If that’s not the case, check the bottle you’re currently using. If it’s old, throw it out.

If you buy sunscreen with the expiration printed only on the box or wrapper, use a permanent marker to write the date somewhere on the bottle. And store it in a cool, dry place. Practice safe sun this summer to keep your family healthy and happy!

Exercise and breathing in summer

Exercising outside on hot, humid summer days might do more harm than good. Find out how to beat the heat!

Exercising outdoors can be uncomfortable and sometimes unhealthy when it’s hot and humid, but there are ways to work out through the weather woes. You’re more likely to breathe faster and deeper and through your mouth—bypassing your nose’s natural filtration system—on hot days. You also risk greater exposure to air pollutants (such as carbon monoxide, particulate matter, and ozone) that can inflame your respiratory system. However, the risks associated with not exercising at all are far greater than the risks of exercising outdoors.

So, plan ahead before exercising outside. And limit your exposure to pollutants, especially on days and in conditions when pollution is bad.

  • Avoid exercising in heavy-traffic areas, such as along highways and during rush hour.
  • During warmer months, exercise earlier in the morning or later in the evening, when ozone levels and temperatures aren’t as high.
  • Check the domestic or international air-quality ratings to determine when it’s safe to exercise outside. Limit your time outside on Code Red and Code Orange days. Environmental conditions on these days aren’t healthy, especially for children, the elderly, and those with existing respiratory conditions.
  • Exercise indoors when the air quality indicates high ozone and particulate levels.
  • Before any demanding physical activity, limit your carbon monoxide exposure by avoiding smoky areas and long car rides in congested traffic.

Distraction-free driving and your teen

As a parent, make sure your teen drives safely and distraction-free this summer.

More teen driving accidents happen during the summer because school is out and teens are driving more—and some are driving while distracted. If the summer sun’s shining and your teen’s asking for the car keys, hand them over cautiously. And do this only after demonstrating safe driving and discussing the danger of driving while distracted.

During the summer months, it’s estimated that 10 people will die each day as a result of accidents involving teen drivers. Distracted driving often leads to crashes. This is especially true for teens distracted by their cell phones, passengers, and other things inside their cars. Anything that takes the driver’s eyes off the road, hands off the wheel, or even mind away from driving is a distraction: Texting and using a cell phone often involves all three.

Distractions impair teens’ driving performance (regardless of their attention spans), reduce safe driving practices, and disrupt traffic flow. If your teen’s friends text and drive—and don’t see a problem with it—your teen is likely to think it’s acceptable and normal.

Discussing the dangers of distracted driving with your teen is an important first step towards prevention. And demonstrating safe, distraction-free driving yourself is key. Teens tend to think their parents are distracted while driving, sometimes more than parents realize.

As a parent, make sure to wear your seat belt, put away your phone, and concentrate on the road. Set driving rules for your teen too (for example, silencing his or her cell phone and putting it away when driving). Review the rules often, and enforce consequences when they’re broken. And ask your teen to sign the pledge, promising to be a safe, distraction-free driver.

Homemade fitness

Your gym workout can be expensive and time-consuming. Use household items to exercise in the comfort of your own home—at little or no cost.

Dumbbells, kettle bells, barbells, and benches can be expensive additions to your home gym. So, get creative, look around your home, and find common household items that can help pump up your fitness routine. Or reuse balls or bottles to boost strength and reduce waste to help protect the environment. Try these DIY home-exercise hacks for a full-body workout that’s convenient and easy on your wallet!

  • Perform calf raises, single-leg raises, or squats on your stairs.
  • Use a sturdy chair for tricep dips, step-ups, push-ups, or squat jumps.
  • Practice ab rollers using a hand or kitchen towel on your tile or hardwood floors, or switch to paper plates for use on a carpet.
  • Use a gallon (or half-gallon) jug—filled with sand to desired weight—for bicep curls, overhead presses, or tricep extensions.
  • Use a 72-oz detergent bottle—weighing about 5 lbs—for 2-handed lifts such as shoulder raises or sumo squats.
  • Use water bottles—filled with water or sand—for a variety of dumbbell-weight exercises, including bicep curls, weight lunges, and shoulder presses.
  • Make a medicine ball: Cut a slit in a basketball or soccer ball, fill with sand, and seal.

Remember there are clever ways to workout—whether you’re on or off duty. And check out HPRC’s videos to learn more home-exercise hacks.




Train in the heat, perform at altitude?

Learn how training in the heat might help you prepare for performance at altitude.

Can you train in the heat to improve your performance at altitude? The answer is “sort of.” “Cross acclimation” or “cross tolerance” is the idea that exposing yourself to one environmental condition can help you adapt to another one as long as they have certain things in common.

As it turns out, this is the case for heat and hypoxia (low oxygen). This is important because athletes and service members can be exposed to altitude without prior or sufficient acclimatization. Altitude sickness can cause several problems, especially decreased performance. But some evidence shows that this method of training in hot conditions to prepare for altitude can actually work.

If you climb to the top of a mountain, there’s less air and less pressure. And you’re getting less oxygen with each breath. This can be simulated at sea level (in special labs) where pressures are normal, but the amount of oxygen in the air is reduced (fake altitude).

However, there’s a bit of a catch. Training in the heat under artificial low-oxygen conditions—normobaric hypoxia or “fake altitude”—involves normal pressure, which is different from “real altitude” or hypobaric hypoxia, which involves reduced oxygen at low pressure. The difference is in the pressure.

So, do these two environments cause the same types of physiological changes? There are several other factors involved in real-altitude acclimatization that might not be accounted for at fake altitude, so the jury’s still out.  

Training in the heat might prepare you for performance at altitude—to a point. Ideally, if you’re going to be at altitude, try to acclimatize yourself as much as you can.

Blisters: Sock it to ‘em

Get off on the right foot! Learn how to prevent blisters.

There are “steps” you can take to protect your feet from blisters. Common among athletes and service members, they might seem like a minor nuisance. However, if left untreated, they can lead to serious infections, sepsis (blood infection), and knee, ankle, or hip injuries.

Blisters result from a combination of friction and moisture. They’ve been blamed on shoe fit or lacing style, but scientific research has shown this isn’t necessarily the case. Common remedies—such as applying antiperspirant or drying powders to the bottom of the foot—aren’t very effective. And in some instances, they can cause irritation, increasing your chances of developing more blisters.

So if friction and moisture are causing problems, then wearing proper socks can bring relief. Look for ones made from acrylic fibers or materials other than cotton, which tends to stay wet. Synthetic materials (nylon, neoprene, and polyester) reduce the amount of shoe-to-sock and sock-to-foot friction by wicking moisture away from your skin. Padded socks also help because they allow for movement within the yarn, reducing frictional forces.

Some evidence suggests wearing a synthetic nylon or polyester liner with an outer-padded wool sock can help prevent blisters. Tip: Try finding your ideal sock before buying boots or shoes because the added bulk might affect the shoe size you need.

You also can reduce your risk of blisters by planning ahead, especially on extremely hot or rainy days. Avoid puddles. Remember to bring an extra pair of socks too. And avoid pouring water on your head since it can drip down into your shoes. Keep your feet happy and blister-free. 

Practice safe sun

HPRC Fitness Arena: Environment, Total Force Fitness
Filed under: Exposure, Heat, Safety, Sun
Learn how to protect yourself from the summer sun while still enjoying time outdoors.

Skin cancer is the most common form of cancer in the U.S., but with proper precautions you can decrease your risk considerably. The sun releases invisible ultraviolet (UV) radiation, which can cause cataracts (clouding of the eye lens) and skin cancers. An estimated 63,000 new cases and 9,000 reported deaths from melanoma—the deadliest form of skin cancer—occur each year.

UV rays also cause tanning and sunburns—and can damage your skin after only 15 minutes of exposure. They weaken the skin’s elasticity, causing wrinkling, rash, and freckles too.

Remember that you can get sun damage on sunny and cloudy days. UV rays penetrate clouds, exposing you to 80% of the sun’s harmful effects. The good news is that you can take steps to protect yourself from UV rays, while enjoying the outdoors.

  • Limit your time in the sun. Seek shade and try to avoid sun exposure during midday (10 a.m. to 2 p.m.) when the rays are strongest. And avoid suntanning and burning.
  • Cover up. Wear protective clothing, including hats, long-sleeved shirts, and pants when going outdoors. Remember that protection decreases when clothes are wet.
  • Apply sunscreen. Use water-resistant sunscreen with Sun Protection Factor (SPF) 15 or higher. Apply and let it absorb 15–30 minutes before heading outdoors. Use lip balm with SPF 30 or higher to protect your lips too. Reapply every 2 hours or after swimming, sweating, or toweling off. 
  • Protect your eyes. Wear sunglasses to cover the skin around your eyes and help prevent eye damage. When choosing sunglasses, check the label to make sure they block 100% of UV rays. 
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