Figure 1. Walk and snow shoveling heart rate curve graph.
NDSU Department of Child Development and Family Science
North Dakota Department of Human Services
June 1999 -- Volume 2, Number 3
Brad Strand, Ph.D. • Department Chair • (701) 231-9718
Donna Terbizan, Ph.D. • Associate Professor • (701) 231-7792
Denis Isrow, Ed.D. • Full Professor • (701) 231-7463All authors work at:
Department of Health, Physical Education and Recreation
Bentson Bunker Fieldhouse
North Dakota State University
Fargo, ND 58105
Please send correspondence to Brad Strand
The purposes of this study were to (1) examine the average heart rates of subjects during 14 minutes of snow shoveling, (2) determine how quickly a subject's heart rate reaches a plateau during snow shoveling, and (3) determine what intensity category snow shoveling fit for young adults. Fifteen volunteer college-aged students engaged in 14 minutes of shoveling snow. Each subject wore a heart monitor to record heart rate during the activity. The average heart rate for subjects during snow shoveling was 153 beats per minute. Subjects reached a heart rate plateau within two minutes of shoveling. Subjects spent ap-proximately 50% of snow shoveling activity at the moderate intensity heart rate level and approximately 35% of snow shoveling activity at the vigorous intensity heart rate level. Subjects were above 90% heart rate reserve for approximately 4% of total activity time.
During the winter of 1996, Fargo, ND received a total of 117 inches of snow, breaking the city's all time snow fall record by 29 inches. As a result, Fargo citizens were required to shovel an extreme amount of snow. Shoveling snow, albeit a good winter workout, can result in a number of different injuries and, in some cases, death. In 1996, it was reported that 1,200 people succumbed to heart disease because of snowstorm related incidents (Franklin, 1997).
The American Heart Association recommends that people who are outdoors in cold weather avoid sudden exertion, like lifting a heavy shovel of snow. Most people are not conditioned to the physical stress of outdoor activities and are unaware of the potential dangers of being outdoors in cold weather, especially when one factors in the wind chill. When individuals fail to take cold weather precautions, hypothermia can quickly result.
The elderly and those with heart disease may be especially at risk. As people age, the ability to maintain a normal internal body temperature often decreases. Because the elderly seem to be relatively insensitive to moderately cold conditions, they can start to suffer the effects of hypothermia without even knowing they are in danger.
Compared to jogging or cross country skiing, there is limited physical action involved in shoveling snow. However, the strain of shoveling puts an increased demand on the heart, with heart rate and blood pressure rising rapidly. This increase requires more oxygen for the heart to function properly, and a person with coronary heart disease, may experience angina symptoms (Hattenhauer & Neill, 1975). Add the body's natural reflex to constrict arteries and blood vessels when it is exposed to cold, and there is potential for heart trouble.
The vast majority of people who go out to shovel their sidewalks will not have a heart attack. But people who have already had a heart attack or who have a history of heart disease, angina, or high blood pressure may want to use caution and common sense when approaching the task. Numerous studies now suggest that strenuous physical exertion after heavy snowfalls may be more deadly than cold air alone (Franklin, Hogan, & Bonzheim, 1995).
The Surgeon General's Report on Physical Activity and Health (U.S. Department of Health and Human Services, 1996) lists snow shoveling for 15 minutes as a moderate intensity activity, using approximately 150 calories of energy. The purpose of this study was to investigate what effect shoveling snow had on heart rate intensities of college-aged individuals. Specifically, we sought to answer three questions: (1) what is the average heart rate of subjects during 14 minutes of snow shoveling? (2) How quickly does a subject's heart rate reach a plateau during snow shoveling? (3) What intensity category does snow shoveling fit into for college-aged individuals?
The subjects were 15 volunteer college-aged students (12 males and 3 females), mean age 21.20 + 2.48 years, mean height 178.64 + 8.23 cm, mean weight 78.06 + 14.45 kg. These subjects were obtained by asking for volunteer subjects from six different courses offered through the Department of Health, Physical Education and Recreation at North Dakota State University. Average resting heart rate for these students was 66.0 + 8.72 beats per minute. All subjects signed informed consent forms and completed a PAR-Q questionnaire designed to screen out individuals who may be at risk for engaging in physical activity.
Polar Vantage XL heart rate monitors (HRM) were used to record heart rate intensity of subjects. The HRM is comprised of two components: a chest band/sensor transmitter and a wrist monitor. The chest band, which contains two wireless electrodes that register the electrical impulse of the heart, is an elastic adjustable strap which secures around the chest by means of a belt lock. The sensor/transmitter, which connects to the chest band, senses the heart beat that is registered by the electrodes and transmits the heart beat signal to the wrist monitor. The wrist monitor is a receiver-microcomputer that receives and displays the information transmitted from the sensor/transmitter, and is able to store that information in 5-, 15-, or 60-second intervals depending on how the wrist monitor is programmed. Stored data were transferred from the wrist monitor to a computer by means of a polar interface unit. Heart rate monitoring has been found to be valid in laboratory and field test use (Leger & Thivierge, 1988; Treiber et al, 1989). In preparation to the actual activity, all heart rate monitors were set to record and store heart rates at a 5-second interval rate.
Subjects were fitted for heart rate monitors, and placed at a starting point on the running track and instructed to compete the Rockport Walk Test (Klein, et al, 1987). This test was designed as a warm-for the snow shoveling activity. Subjects were instructed to walk one mile (seven laps on the track) as fast as possible.
At the completion of the walk test, subjects rested until their heart rates recovered to below 110 beats per minute. After resting for approximately 10 minutes subjects moved outside to begin shoveling snow. All subjects used a flat snow shovel with a 16-inch face. Subjects stood facing a snow drift and were instructed to shovel snow from the drift and throw it over a 4-foot fence in front of them. They continued this action for 14 minutes.
Upon completion of the walk test and snow shoveling, heart rate data were downloaded via a Polar interface. The Polar statistics package was used to determine minutes of time, percentage of time, and means of the heart rate data for the Rockport Walk Test and for snow shoveling. Figure 1 shows a sample of the downloaded data.
This study was designed to answer three specific questions regarding the effects of snow shoveling on heart rate intensities of college-aged students. What follows are the answers to those three questions.
The first research question asked, What is the average heart rate of subjects during 14 minutes of snow shoveling? Results revealed that subjects achieved an average heart rate of 153 + 15.95 beats per minute during the 14 minutes of snow shoveling. This heart rate average places subjects within the moderate heart rate intensity (51-70% of HRR) for snow shoveling.
The second research question asked, How quickly does a subject's heart rate reach a plateau during snow shoveling? In this study subjects reached a heart rate plateau in 1.99 + 0.72 minutes of snow shoveling, ranging from 1 minute to 4 minutes. The subjects then maintained that intensity of activity for the duration of the activity. Figure 1 provides an example of how sharply one subject's heart rate rose once he or she began shoveling snow. As noted, snow shoveling began at approximately the 22 minute mark on this particular curve graph and continued until the 36 minute mark.
Figure 1. Walk and snow shoveling heart rate curve graph.
Research question three asked, What intensity of activity category does snow
shoveling fit into for college-aged individuals? Heart rate intensities were broken down
into five levels: 0 - 30% of heart rate reserve (HRR), 31 - 50% HRR, 51 - 70% HRR, 71 -
90% HRR and > 91% HRR. These levels were calculated for each subject, and then applied
to each individual heart rate record. A heart rate reserve of 51 -70% indicates a moderate
intensity while a heart rate reserve above 71% indicates a vigorous intensity level.
As seen in Table 1, during the snow shoveling activity, subjects spent an average of 0.08 + 0.17 minutes (0.47%) in the first intensity level, 1.67 + 2.68 minutes (12%) in the second level, 7.51 + 4.45 minutes (52.73%) in the third level, 4.44 + 4.34 minutes (31.07%) in the fourth level, and 0.52 + 1.89 minutes (3.53%) in the fifth level.
Table 1. Average time in minutes and percentage spent during snow shoveling and
walking at different heart rate intensities.
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Heart Rate Reserve Intensities
---------------------------------------
Activity 0-31% 31-50% 51-70% 71-90% >91%
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Snow Shoveling
Minutes 0.08 1.67 7.51 4.44 0.52
Percentage 0.47 12.0 52.73 31.07 3.53
Rockport Walk Test
Minutes 0.59 4.39 5.17 2.53 0.00
Percentage 3.53 28.6 40.87 20.47 0.00
--------------------------------------------------------
As can be noted, subjects spent the majority of their time (52.73%) during the snow
shoveling activity in the moderate intensity heart rate level. However, subjects did spent
34.6% of their time at a vigorous intensity level or higher, defined as above 71% of heart
rate reserve. Additionally, subjects worked with a heart rate greater that 91% of heart
rate reserve for approximately 4% of total activity time.
Almost everyone living in North Dakota will at some point be faced with snow shoveling. The question becomes, who should not shovel snow? Gibson, Cooper & Meyer (1980) have suggested that it is the combination of vigorous physical exertion and a diseased or susceptible heart, rather than the exertion itself, that puts the cardiovascular system at risk. However, in 16% of all heart attacks, "the first, the last, and the only symptom" of coronary distress is sudden cardiac death (Franklin, 1997). Individuals over age 40 with a history of heart disease, symptoms that suggest a cardiac disorder (dizziness, chest pain, abnormal heart rhythm), or one or more major coronary risk factors (cigarette smoking, high blood pressure, elevated blood cholesterol, or sedentary lifestyle) should be cautioned regarding the potentially threatening cardiac demands and associated stresses of snow shoveling (Franklin, 1997).
This exploratory study was designed to investigate what effect the shoveling of snow had on the heart rate intensity of healthy college-aged students. Results indicate that these particular subjects: 1) obtained an average heart rate of 153 beats per minute, 2) reached a heart rate plateau in slightly less than two minutes of shoveling, and 3) spent approximately 50% of their activity time at a moderate level of heart rate intensity and 35% of their activity time at a vigorous level of heart rate intensity. Comparatively, during the approximately 14 minutes of warm-up (Rockport Walk Test), subjects reached an average heart rate of 140 beats per minute and spent approximately 40% of their activity time at a moderate level of heart rate intensity and 20% of their activity time at a vigorous level of heart rate intensity.
The data obtained in this study support the Surgeon General's Report classification of snow shoveling for 15 minutes as a moderately intense activity for this age group based on average heart rate during the activity. Whether this is true for other age groups has yet to be investigated. Further, the data substantiate the statement that an individual's heart rate does rise rapidly during snow shoveling and continues to rise during the activity if rests are not taken. All subjects in this study were very healthy college-aged students; an older population or one with heart disease may expect to see an even more dramatic spike in heart rate. This should be reason for concern in that sudden physical exertion by unhealthy middle-aged individuals and senior citizens has been indicated to cause problems such as angina, shortness of breath, dizziness, chest pain, abnormal heart rhythm, and death.
Finally, even though the data show that snow shoveling should be classified as a moderate intensity activity based on average heart rate during the activity, it is interesting to note that snow shoveling subjects were working at a vigorous intensity level for more than one-third of their total activity time. And further, subjects spent 4% of their activity time above 91% of heart rate reserve. This would indicate that these subjects were at times working as hard as if he or she were running a sprint that demanded total physical exertion. Whether this division of activity level is accurate for an older or an unhealthy population has yet to be investigated.
The next step in this line of research will be to replicate this study. If similar findings are found the authors will design additional studies that investigate the effects of shoveling snow on individuals from different age groups and with different fitness levels; studies that compare the effects of moving snow with different sized shovels as compared to using snow blowers; and studies that compare the effects of moving snow in different temperatures while wearing various types of clothing and with various depths of snow. In addition, further studies will also investigate other physiological responses, such as blood pressure and caloric expenditure, in relation to the effects of shoveling snow.
The results of this study appear to indicate that snow shoveling may be a good moderate intense activity for healthy college-aged students. However, the study also revealed that the shoveler's heart rate spikes suddenly and dramatically upon commencing snow shoveling; the heart rate stays elevated for the duration of the activity; and that one may work at a very vigorous intensity level during the activity. Based on these facts, several recommendations (Strand, Scantling & Johnson, 1997) are noted for individuals who engage in winter activity such as shoveling snow:
Franklin, B. A. (1997). Prevention of heart attacks during snow shoveling. ACSM's Health & Fitness Journal, 1(6), 20-23.
Franklin, B.A., Hogan, P., Bonzheim, K., Bokalyar, D., Terien, E., Gordon, S., Timmis. G. (1995). Cardiac demands on heavy snow shoveling. Journal of the American Medical Association, 273, 880-882.
Gibbons, L.W., Cooper, K.H., & Meyer, B.M. (1980). The acute cardiac risk of strenuous exercise. Journal of the American Medical Association, 244, 1799-1801.
Hattenhauer, M., & Neill, W.A. (1975). The effect of cold air inhalation on angina pectoris and myocardial oxygen supply. Circulation, 51, 1053-1058
Klein, G.M., Porcari, J.P., Hintermeister, R., Freedson, P.S., Ward, A., McCarron, R.F., & Ross, J. (1987). Estimation of VO2 max from a one-mile track walk, gender, age and body weight. Medicine and Science in Sports and Exercise, 19(3), 253-259.
Leger, L., & Thivierge, M. (1988). Heart rate monitors: Validity, stability, and functionality. The Physician and Sports Medicine, 16(5), 143-151.
PAR-Q Validation Report, British Columbia Department of Health, June 1975.
Polar Electro Oy. POLAR Heart rate Analysis Software for Apple Macintosh Computers, 1993.
Strand, B.N., Scantling, E., & Johnson, M. (1997). Fitness education: Teaching concepts-based fitness in the schools. Boston, MA: Allyn & Bacon, Inc.
Treiber. F.A., Musante, L., Hartdagan, S., Davis, H., Levy, M., & Strong, W.B. (1989). Validation of a heart rate monitor with children in laboratory and field settings. Medicine and Science in Sports and Exercise, 21, 338-342.
U.S. Department of Health and Human Services. (1996). Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion.
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The North Dakota Journal of Human Services, June 1999 -- Volume 2, Number 3