Exercise in the heat

Exercise in the heat

by Mr A. E. Hoosen

As people become more aware of the value of exercise, it is important to understand the safety issues surrounding exercise. As we near the summer months, people want to shed those excess centimetres here and there to look good for the beach. As a result more people take to the road to jog or run and even more are in the gyms. In light of the past week we have had in Gauteng, we shall evaluate how to exercise in the heat.

We must first look at the factors that influence heat; conduction, convection, evaporation, radiation, metabolic heat.  Conduction is the transfer of heat from one body to another via direct contact, convection is the transfer of heat, radiation is the transfer of heat from one body to another via electromagnetic waves and evaporation is heat loss via the change in phase of water from a liquid to a gas. These factors can either positively or negatively alter heat balance and in combination can result in heat gain or heat loss except for evaporation. Evaporation exclusively favours heat loss and thus promotes cooling. In the case of the exercising individual, sweating is the most important means through which we lose heat, as the sweat formed evaporates from the skin cooling the skin. If the sweat drips off the skin, that potential of the sweat to reduce heat is diminished. 

FACT80% of heat lost during exercise is due to evaporation of sweat

Now that we have identified the factors that influence heat, we need to identify how hot is hot? 23°C on a sunny day vs 23°C on a cloudy and windy day. This is why we use the heat index, to level the playing field as the environmental heat is more than just absolute temperature. We need to take into account; radiation (sun), humidity, air velocity (wind) and air temperature readings in combination. This can provide us with the apparent heat of the day. Apparent

Temperature Range                                     Dangers/Precautions at This Range

27°C–32°C                            Exercise can be difficult; enforce rest and hydration

32°C–41°C                            Heat cramps and exhaustion; be extremely cautious

41°C–54°C                            Anticipate heat exhaustion; strictly limit activities

54°C and above                    Setting for heatstroke; seek cool shelter

In order to calculate the apparent temperature one can obtain the current temperature and either dew point temperature or humidity and you can use the online calculator at: http://www.hpc.ncep.noaa.gov/html/heatindex.shtml

How does the body respond to exercise in the heat?

Let us look at the cardiovascular system, the heart pumps blood to the body, and during exercise blood flow is directed to the muscles to meet energy demands, however with exercise the body generates heat and some blood is directed away from the muscles to the skin. This allows the body to dissipate heat via convection, radiation and evaporation. However in the heat the body transfers more blood to the skin to accelerate heat loss in an attempt to keep cool, this results in the heart speeding up the rate of pumping, and results in a phenomenon called cardiovascular drift. Cardiovascular drift is whem heart beats so fast that instead of pumping out more blood, less blood is pumped per beat.

The second means of dissipating heat is through sweat loss. Sweat production draws from the water located in the plasma of the blood. When one exercises for a prolonged period of time without replacing fluids, the blood becomes more viscous, resulting in less blood being able to pass through the body reducing the supply of oxygen and nutrients to the muscle. These two factors can hamper performance and can in combination pose a health risk.

Guidlines to Exercise in the heat:

1.       Exercise in the mornings and evenings.

2.       Drink plenty of fluids even when not thirsty every 15-30minutes (Isotonic replacement)

3.       Clothing

              a. Clothing that allows ventilation

              b. Wear light coloured clothes

              c. Cover small surface area of the body (expose maximum surface area)

              d. Hats for extreme sunlight

4.       Utilise sunblock

5.       Avoid exercise when heat index is 32^oC or more

6.       Avoid consuming salt tablets or foods high in salt

WARNING SIGNS OF HEAT EXHAUSTION

• Heavy sweating
• Fatigue
• Headache
• Pale, clammy skin
• Thirst
• Rapid heartbeat
• Dizziness, fainting
• Nausea, vomiting
• Muscle and abdominal cramps 
• Mild temperature elevations

If one experiences the following conditions, move to a cooler shady area, drink cool liquids and seek medical attention immediately. Now that summer is at the door step we can now exercise safely

20th October – WORLD OSTEOPOROSIS DAY

By Bailey Cockerill

Defⁿ: Osteo – Bone; Porosis – Porous

A porous bone disease resulting in a high risk of bone fracture

Osteoporosis is considered to be one of the most common bone diseases and is easily preventable if you know the do’s and don’ts. Prevention, in this instance is without doubt better than cure!

What Causes Osteoporosis?

Throughout our lives the skeletal structure is continuously being remodeled with old bone tissue being removed (resorbed) and laid down (reformed). Unfortunately the bone reformation process is slowed down the older we get resulting in more resorbtion occurring and less bone density resulting. Once women reach menopause and there is a resultant drop in oestrogen levels, an accelerated bone loss can be noticed. This is not to say that men are not equally at risk as once testosterone levels begin to drop, they too can be at higher risk.

Who is at Risk?

• Females (not that males aren’t though!!)  
  
• Smokers  
  
• Individuals with inadequate caloric intake  
  
•  Inactive individuals
  
• Ammenorrhoeric females (prolonged absence of menstrual cycle usually associated with overly active female athletes) – Balance is key  
  
• Early onset of menopause

Prevention?

Healthy diet with adequate amounts of calcium. Remember that Vitamin D is needed to help absorb calcium – you can’t have one without the other!

Limit smoking, caffeine and alcohol intake as they may lead to increased bone loss. 

Do weight bearing exercises (eg. walking, jogging, resistance exercises etc) Not only does it help with actual bone density, but also improves balance which is imperative in helping prevent falls that can result in serious fractures if already struggling with osteoporosis.

Have regular checks for your bone density. A DEXA scan is the most accurate form of screening.

Other risk factors include a family history of osteoporosis and age associated changes in sex hormones. However these are obviously unavoidable and just need to be taken into consideration.

So, start early with a healthy diet, regular exercise and limit intake of caffeine, alcohol and smoking to keep your bones strong and healthy!

General Exercise Guidelines from the American College of Sports Medicine

by Lauren Williamson

The American College of Sports Medicine (ACSM) recently updated its position stand on the quantity and quality of exercise for healthy adults. For improvement of cardiovascular fitness and body composition, they recommend performing physical activity 3 - 5 times each week for 20 - 60 minutes at a time. That therefore means a minimum of 60 minutes per week of physical activity. Exercise sessions should involve activities that involve large muscle groups (e.g., walking, running, cycling, and swimming).

The intensity level (target heart rate) for this physical activity should be at least 55% - 65% of your maximum heart rate. (You can estimate your maximum heart rate by subtracting your age from 220.) You can quickly determine if your intensity is too high by taking the "talk test"; if you cannot maintain a conversation with your exercise partner while exercising, then your intensity is too high. The ACSM also recommends that you include muscular strength and flexibility training in your exercise program.

If you are not currently exercising, please consult your physician before beginning any exercise program. If you’ve been given the all-clear to exercise, start off at a comfortable training pace and slowly increase your intensity, frequency and duration of training.

REMEMBER! Consistency is the key to success in any exercise program; choose an activity that you enjoy and are likely to continue throughout your adult life.

The Silent Killer

By Nicole Picas

Hypertension, more commonly known as high blood pressure, has been nicknamed ‘the silent killer’ because there are no noticeable symptoms, but its presence can be fatal. An individual with hypertension is at an increased risk for renal (kidney) disease, cardiovascular disease and stroke. The table below classifies blood pressure for adults aged 18 years and older.

Category	Systolic BP (mmHg)	Diastolic BP (mmHg)
Optimal	< 120	< 80
Normal	< 130	< 85
High-normal	130-139	85-89
Hypertension      Stage 1      Stage 2      Stage 3	140-159 160-179 180	90-99 100-109 110

Adapted from ACSM’s Exercise Management for Persons with Chronic Diseases and Disabilities, Second Edition, 2003.

Systolic blood pressure refers to the pressure in the blood vessels when the heart is contracting. Diastolic blood pressure refers to the pressure in the blood vessels when the heart is relaxed. Hence, high blood pressure puts undue strain on the heart. ACSM identifies the following risk factors for hypertension: obesity, high sodium intake, smoking and inactivity. All efforts should be made to modify lifestyle first, but medication may be administered immediately when necessary. It is important to note that hypertension generally does not occur in isolation; often other pathologies exist, such as high cholesterol and insulin resistance.

Exercise plays an important role in managing cardiovascular disease and hypertension by improving cardiovascular fitness, increasing circulation and relieving stress. The following exercise guidelines can be used for persons with hypertension:

·        Increase aerobic activity (walking, jogging, cycling, rowing, etc.) – try to do at least 30-45 minutes 3-5 times per week

·        Avoid heavy weights

·        Avoid movements that involve lifting weights above your head

·        Remember to breathe throughout exercises – don’t hold your breath!

Remember: check your blood pressure on a regular basis so that preventative measures can be taken before the silent killer strikes!