Human and Environmental Factors PDF

Human and Environmental Factors  HUMAN FACTORS Age Gender Height Weight Body Mass Index Body Fat Percentage Heart Rate Strength Dexterity Body Mass Index (BMI) Defined as the body mass divided by the square of the body height, and is universally...

Human and Environmental Factors  HUMAN FACTORS Age Gender Height Weight Body Mass Index Body Fat Percentage Heart Rate Strength Dexterity Body Mass Index (BMI) Defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m2 A frequent use of the BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person of his or her height. BMI categories are generally regarded as a satisfactory tool for measuring whether sedentary individuals are underweight, overweight or obese with various exceptions, such as: athletes, children, the elderly, and the infirm Limitations: BMI ignores scaling law BMI ignores variation in physical characteristics BMI does not differentiate between muscle mass and fat mass Body Fat Percentage the total mass of fat divided by total body mass a measure of fitness level, since it is the only body measurement which directly calculates a person's relative body composition without regard to height or weight Body fat Essential fat the minimum amount of fat necessary for basic physical and physiological health Storage body fat consists of fat accumulation in adipose tissue, part of which protects internal organs in the chest and abdomen *American Council on Exercise BFP measurement techniques Anthropometric methods Skinfold methods Ultrasound Height and circumference methods From BMI Child body fat % = (1.51 × BMI) − (0.70 × Age) − (3.6 × sex) + 1.4 Adult body fat % = (1.20 × BMI) + (0.23 × Age) − (10.8 × sex) − 5.4 *where sex is 1 for males and 0 for females Bioelectrical impedance analysis a lower-cost but less accurate way to estimate body fat percentage two or more conductors are attached to a person's body and a small electric current is sent through the body; The resistance between the conductors will provide a measure of body fat between a pair of electrodes Heart Rate the speed of the heartbeat measured by the number of contractions of the heart per unit of time — typically beats per minute (bpm) The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide. Activities that can provoke change include physical exercise, sleep, anxiety, stress, illness, ingesting, and drugs Measurement: Manual – pressuring of body pulse points with index and middle fingers Electronic (e.g. ECG, heart rate monitors) Resting heart rate The basal or resting heart rate (HRrest) is defined as the heart rate when a person is awake, in a neutrally temperate environment, and has not undergone any recent exertion or stimulation, such as stress or surprise. The typical resting heart rate in adults is 60–100 beats per minute (bpm). Heart rate recovery is the reduction in heart rate at peak exercise and the rate as measured after a cool-down period of fixed duration. A greater reduction in heart rate after exercise during the reference period is associated with a higher level of cardiac fitness. Heart rates that do not drop by more than 12 bpm one minute after stopping exercise are associated with an increased risk of death. Muscular Strength the ability to exert force on physical objects using muscles Types: Isometric strength Static exertion of strength Dynamic strength Muscular exertion which produce motion about a joint Factors affecting muscular strength Personal factors (age, gender, anthropometry, motivation) Task influences (posture, duration of exertion, velocity of contraction, muscle fatigue) Environmental influences (temperature, humidity) Dexterity the coordination of small muscle movements—usually involving the synchronization of hands and fingers—with the eyes Classifications Dexterity among fingers Between thumb and index finger Among thumb, index finger and middle finger Among all fingers Dexterity between hand and other parts Between wrist and hand Between two hands Visual Acuity a measure of the resolving qualities of the eye (ability to see fine detail). Affected by physiological factors such as receptive ability of the visual receptors. Integrity of the nerve pathways to the brain. CHERNCK (1983) considers the following visual skills important: a) Visual acuity b) Near point of convergence (i.e. the closest point to the person along the median line at which he can continue to fixate the target with both eyes). c) Stereopsis (i.e. the perception of three-dimensional visual space as a result of binocular cues). d) Fusion (i.e. the integration of two similar ocular images into a single precept). e) Colour Vision f) Accommodative facility (i.e. the ability to change focus efficiently from near to far and back again). g) Eye movement ability (i.e. the ability to follow a moving target smoothly, keeping both eyes on the target). h) Visual motor integration (i.e. co-ordination between the eyes and the extra-ocular muscles).