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Walking Extravaganza!

Research-based answers to seven questions covering physiology to program design will help your clients move past pedestrian pace to meaningful challenge and results.

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We all know the basics on walking: It’s simple, inexpensive and brimming with health benefits. The scientific literature backs this up, concluding that the cumulative effects of walking can reduce the risk of developing coronary heart disease, help in the treatment of hypertension, improve insulin/glucose metabolism for the prevention or management of type 2 diabetes and aid in the treatment of some musculoskeletal diseases (Hu et al. 1999; Lee et al. 2001; Morris & Hardman 1997).

Yet, in an age when exercise technology is increasingly complex and trainers’ clients are developing more sophisticated tastes, questions linger: How can walking provide a worthwhile workout, and how well does walking burn calories? These and many other walking-related issues are explored in this review, which highlights research understandings on calorie burning and presents several evidence-based ideas for incorporating newer strategies in your walking exercise program designs.

As you read this report, take a moment to check out the sidebars:

  • Adapting High-Intensity Interval Training Programs to Walking
  • Calorie Expenditure and the Science of Calorimetry
  • Joint Stress With and Without Load

Traditional walking strategies are not for everyone. They might not provide enough challenge to people of above-average fitness, or they may be too difficult for those who suffer from ambulatory physical limitations. Still, walking is excellent exercise for a broad cross-section of the population. The following seven questions address key topics about walking:

1. What Is an Adult’s Natural Walking Pace, and Why?

Most healthy adults tend to naturally select a walking pace of approximately 2.8 miles per hour (Willis, Ganley & Herman 2005). Researchers hypothesize that the central nervous system selects a preferred walking speed to lessen the body’s energy expenditure (Martin, Rothstein & Larish 1992). Another theory is that preferred walking speed reflects changes in fuel use: In most adults, fat is the primary fuel source at speeds up to 2.8 mph, which serves as a metabolic walking threshold speed (Willis, Ganley & Herman 2005). Above this speed, carbohydrate oxidation (breakdown) increases rapidly, resulting in a perception of greater effort because carbohydrates are a limited fuel source compared with fat. As a result, preferred walking speed appears to happen naturally, as the body seeks out the most economical fuel conditions in the muscle when fat oxidation is the primary fuel source. See Figure 1.

Aging and inactivity often diminish the musculoskeletal functioning of the lower-body gait muscles (Martin, Rothstein & Larish 1992). This may require the body to recruit additional motor units and perhaps a higher proportion of less-economical fast-twitch muscle fibers (which are fueled predominantly by carbohydrate) in order to generate the force required for walking. This is why the elderly see a decline in walking speed and a change in gait characteristics.

2. What Is “Brisk” Walking?

Exercisers are often urged to take a “brisk” walk, but the idea of a “brisk” pace is open to interpretation. A brisk walk for some is a leisurely stroll for others.

A good starting point is the American College of Sports Medicine’s (ACSM 2014) recommendation that most adults accumulate 30–60 minutes a day of moderate-intensity exercise at least 5 days a week, or 20–60 minutes a day of vigorous-intensity exercise at least 3 days a week—or a combination of the two.

How do walking exercisers determine whether their moderate-intensity walk meets ACSM guidelines? Scientifically, walking at an intensity of 3–6 METs (metabolic equivalent of task is a physiological measure expressing the energy cost of physical activities) is considered moderate-intensity exercise. Counting steps is another practical way to measure intensity. Marshall et al. (2009) determined that walking at approximately 100 steps per minute is moderate-intensity exercise. At 100 steps per minute, a walker can meet current recommendations for moderate-intensity physical activity by walking at least 3,000 steps in 30 minutes at least 5 days a week. This can easily be tracked with any pedometer or pedometer app on a smartphone. A walker could also accumulate three daily walks of 1,000 steps in 10 minutes on 5 days each week.

Murtagh, Boreham & Murphy (2002) examined 82 recreational walkers who selected their own perceptions of a “brisk” walking pace. Overall, the subjects walked at an average of about 3.5 mph and were able to accurately reach moderate-intensity exercise levels by self-selecting their pace. Older adults (aged 60–85 years) had an average self-selected walking pace of 3.3–3.5 mph (Parise et al. 2004). So there you have it: “Brisk” is an accurate description of a moderate-intensity walk, although the actual pace may vary depending on age and individual
fitness level.

3. How Does Load Placement Affect Caloric Expenditure of Walking?

There are plenty of ways to add weight to the body while walking: Carrying hand weights is one way; wearing a backpack, ankle weights or a weighted vest are others. However, not all methods of adding load have the same effect on energy expenditure.

Much of the energy cost of walking results from activating the muscles that control the body’s center of mass, swinging the legs relative to the center of mass and supporting body weight (Griffin, Roberts & Kram 2003).

Changing the position of a load can shift rotational torque on the body’s center of mass, creating differences in muscle activation and metabolic cost; so not all forms of a given mass will produce equal amounts of energy expenditure (Watson et al. 2008). Exercise professionals will need to make clear to their clients that different forms of loaded exercise can cause widely variable caloric demands.

Carrying a weight of up to 18% body weight in one hand demands more energy than distributing the same total weight between both hands. However, this asymmetrical loading is a very complex behavior in terms of balance (Watson et al. 2008), and thus for most exercise enthusiasts it is not a safe option during sustained walking. It may be acceptable for short (1-minute) spurts of walking in a circuit class or in metabolic training.

4. Have You Heard of the “Free-Ride” Phenomenon?

The “free-ride” walking phenomenon attracted attention in the mid-1980s from researchers fascinated by the huge loads that African women could carry on their heads. This ability is known as head-loading. Researchers found that African women who were experienced in head-loading could carry up to 20% of their body mass without expending any more energy than they used when walking unloaded (Maloiy et al. 1986). This gave rise to the “free-ride hypothesis,” which posited that a load up to a certain weight could be carried on the head without any extra energy expenditure.

The researchers speculated that “some element of training and/or anatomical change since childhood may allow these women to carry heavy loads economically” (Maloiy et al. 1986). A more recent study comparing less-experienced African women head-loaders with women without any head-loading experience challenges this free-ride hypothesis (Lloyd et al. 2010). The phenomenon requires further study.

Researchers have also explored whether carrying a backpack generates energy savings. Abe, Yanagawa & Niihata (2004) observed an energy-saving effect when subjects carried a backpack at a load equal to 15% of body mass during slow walking (<3.35 mph); however, this effect ceased at walking speeds above 3.35 mph.

A similar energy-saving effect was observed when loads were carried in the hands (6.5–13.5 pounds in each hand) during slower walking speeds. Abe and colleagues concluded that total energy costs to the body from hand and arm muscles holding weights during slow walking are negligible. Additionally, and perhaps more importantly from a safety standpoint, it becomes problematic to even grip or hold traditional dumbbells (or kettlebells) for a sustained period like a 30-minute walk. Thus, this is not a worthy option for exercise professionals to recommend to their clients.

5. Does Wearing a Weighted Vest While Walking Burn More Calories?

Weighted vests are gaining attention from exercise professionals and fitness enthusiasts. The vests (typically equal to 5%–20% of a person’s body weight) can be used in many types of workouts, and most vests can be adjusted to add or subtract weight as desired. Further, weighted vests are worn over the shoulders, making them a more natural addition to an exerciser’s center of gravity.

In a 2006 study, Puthoff et al. examined walking energy expenditure at incremental treadmill speeds ranging from 2.0 to 4.0 mph and vest weights ranging from 10% to 20% of body mass. The researchers found that energy expenditure increased as vest weight and walking speed increased; however, the relationship between vest weight and walking speed was not entirely linear. As walking speed increased, wearing a weighted vest had a more pronounced impact on energy expenditure.

These findings have many practical implications in the design of walking programs. For instance, walking at slow speeds may require the exerciser to use a heavier vest to achieve the desired increases in energy expenditure, while walking at faster speeds will produce a more pronounced increase in energy expenditure with less weight needed to generate the increase.

Additionally, walking with a weighted vest may be beneficial for those who cannot walk briskly, as adding just 10% of body mass at a slower walking speed (~2 mph) may produce relative exercise intensity similar to walking faster without added mass. Thus, using a weighted vest is a viable way to increase exercise intensity for all fitness levels, and it’s a strategic training approach that exercise professionals can incorporate into their clients’ exercise programs. In fact, research is underway to better identify the optimal vest weight, walking speed and treadmill incline combinations for greater energy expenditure.

6. What About Inclined Treadmill Walking?

Increasing the incline while walking on a treadmill is a common way to add to the intensity of walking exercises, especially for those who can’t reach faster walking speeds or for obese populations for whom joint-loading injuries are a concern. Ehlen, Reiser & Browning (2011) found that with the addition of inclines between 6% and 9%, obese people could achieve an adequate exercise stimulus for weight management at speeds as low as 1.7 mph.

Additionally, slower walking at a moderate incline reduced the load placed on the lower-extremity joints in comparison with faster walking (~3.35 mph). Incline walking may also be appropriate for older populations or for those suffering from joint problems. There are no standard recommendations for inclines in walking bouts, so exercise professionals are encouraged to establish appropriate treadmill incline settings based on the fitness levels and perceived efforts of each client.

7. Walking vs. Running: What’s the Impact on Caloric Expenditure?

A fundamental principle of physics is that movement of a specific mass over a given distance requires a specific amount of energy, no matter how fast the mass is moving. Thus, in theory, walking or running a given distance should require the same amount of energy regardless of speed (Hall et al. 2004). While this principle is sometimes observed in four-legged animals running a mile compared with moving at a leisurely pace (Kram & Taylor 1990), humans tend to expend more energy when running (~30% higher depending on intensity) than when walking the same distance (Hall et al. 2004). More research is needed to better clarify this comparison.

Conclusion

With proper modifications, walking programs can be tailored to meet the needs of clients at all fitness levels, with the added benefit of causing less joint stress than high-impact exercises do. There are many ways to alter walking programs to meet the target intensities of exercisers at all fitness levels. Possible adjustments include walking at different speeds, wearing weighted vests while walking, changing the incline while on a treadmill and adapting existing interval-training programs to walking.

Exercise professionals are encouraged to incorporate and combine any of these modifications to meet their clients’ needs and goals. Keep on walking!



Figure 1. How Does the Body Choose Its Natural Walking Speed?

Our natural walking speed is generated by the central nervous system, which seems to choose the most economical walking gait for optimal use of fat as a fuel (Willis, Ganley & Herman 2005).

Figure 2. Key Practical Application Findings From the Walking Research

Feet and ankle weights increase energy expenditure but may also result in harmful overuse and repetitive-stress injuries.

Walking 100 steps per minute equates to moderate-intensity exercise.

Weighted vests (5%-20% of body weight) meaningfully increase the energy expenditure of walking.

Carrying weights in both hands (up to 13.5 pounds in each hand) when walking at slower speeds (up to 3.4 mph) is ineffective for increasing energy expenditure.

Carrying asymmetrical weight (weight in one hand) is a complex balance challenge and is not recommended for sustained walks.

Adapting HIIT programs from other modes of exercise is an excellent strategy for varying walk programs.

Adapting High-Intensity Interval Training Programs to Walking

Numerous high-intensity interval training research studies have explored jogging, running and cycling for exercise. Walking programs may be readily developed based on the findings of these studies.

The programs below adapt the intensity of intervals for walking, using guidance from the Rating of Perceived Exertion Scale (see Figure 3). All five of these HIIT examples draw on research-based interval programs, but personal trainers should modify them according to the fitness level of the individual. Remind clients to complete an appropriate warm-up and cool-down with every walking workout.

1. High-Intensity Aerobic Interval Walking

Protocol. Complete up to 10 high-intensity walking intervals lasting 4 minutes each, interspersed with 2-minute relief walking intervals.

Intensity. Perform the 4-minute high-intensity intervals at a Hard (15 RPE) to Very Hard (17 RPE) intensity level, and perform the relief interval at a Light (11 RPE) level. Use walking speed or treadmill incline (or a combination of both) to vary walking intensity.

Duration. About 1 hour.

Source: Perry et al. 2008.

2. Sprint Interval Walking

Protocol. Complete 4-6 sprint walking intervals lasting 30 seconds each, interspersed with 4.5 minutes of light walking at a self-selected pace.

Intensity. Do the sprint walks at a near-maximal walking intensity, which would suggest in the range of Very Hard (17 RPE) or slightly harder (18 RPE). Complete the self-selected 4.5-minute walking recovery period at a Very Light (9 RPE) level.

Duration. 20-30 minutes.

Source: Burgomaster et al. 2008.

3. Step-Wise Interval Walking

Protocol. Start at a relatively easy walking workload for 5 minutes of exercise, then increase intensity about 15% for 4 minutes and continue to increase intensity every 4 minutes. This program can be halted at a particular intensity level or after a specific duration; it should be followed by a cool-down walk.

Intensity. Initial walk intensity should have an RPE of 11. Then increase the intensity roughly 1 RPE with each subsequent 4-minute stage by increasing walking speed or treadmill incline, or by a combination of the two. For example, this program starts at an RPE of 11; after 4 minutes the intensity becomes a 12 RPE; after another 4 minutes the intensity becomes a 13 RPE; and after another 4 minutes the intensity becomes a 14 RPE. Continue until a specific time or intensity level is achieved.

Duration. Follow ACSM (2014) guidelines, which recommend 20-60 minutes of continuous cardiorespiratory exercise.

Source: Jacobs & Sjodin 1985.

4. Near-Maximal Interval Walking

Protocol. Perform a 5-minute near-maximal intensity walk, followed by a 5-minute recovery walk; repeat.

Intensity. The near-maximal walking interval is around 17 on the RPE scale. The recovery interval is between 11 and 12. Use walking speed or treadmill incline to vary the intensity.

Duration. Follow ACSM (2014) guidelines, which recommend 20-60 minutes of continuous cardiorespiratory exercise.

Source: Gormley et al. 2008.

5. Supramaximal Interval Walking

Protocol. Complete 7-10 sprint walking intervals lasting 90 seconds, interspersed with 30 seconds of walking at a self-selected pace.

Intensity. Do sprint walks at a very challenging but sustainable walking pace, which would suggest a Very Hard (17 RPE) intensity. Complete the self-selected 30-second walking recovery interval at about a Very Light (9 RPE) level.

Duration. 20-30 minutes.

Source: Gosselin et al. 2012.

Figure 3. Rating of Perceived Exertion Scale
 
6 No Exertion At All: This would be analogous to sitting and relaxing.
7 Extremely Light: This is very easy standing movement.
8  
9 Very Light: This is similar to casual walking.
10  
11 Light: This is comparable to the intensity of a light warm-up.
12  
13 Somewhat Hard: This is a workout intensity that feels mildly challenging.
14  
15 Hard: This is a workout intensity that feels difficult.
16  
17 Very Hard: This is a very demanding workout intensity.
18  
19 Extremely Hard: This is a rigorous intensity that cannot be maintained.
20 Maximal Exertion: This is an all-out exercise exertion.
Calorie Expenditure and the Science of Calorimetry

The term calorimetry, meaning the science of measuring caloric expenditure, comes from the Latin word calor, meaning heat, and the Greek word metron, meaning measurement. This science is built around an understanding that cellular energy, in the form of ATP (adenosine triphosphate) from carbohydrates and fats, is about 40% efficient for muscular work, with 60% of the energy degrading to heat. Because heat production equals the rate of cellular reactions for work, measuring heat allows an accurate estimate of energy expenditure.

The science of calorimetry dates to the late 18th century. In the 19th century, scientists added the use of devices called bomb calorimeters: sealed metal chambers surrounded by a container holding a known volume of water. Heat flow from the combustion of food in the chamber crosses the wall and heats the container of water, which is used to measure the heat change.

Direct Measurement
Bomb calorimeters offer a direct form of calorimetry, as scientists can ignite a food source directly within an oxygen-rich environment to measure the heat released. A kilocalorie is the amount of heat required to raise the temperature of 1 kilogram (about 33.8 ounces, or 1 liter) of water by 1 degree from 14.5 degrees Celsius (58 degrees Fahrenheit) to 15.5 degrees Celsius (60 degrees Fahrenheit). Burning food under controlled conditions in the bomb calorimeter breaks chemical bonds, releasing free energy and heat. This burning is chemically similar to the metabolic breakdown of food in cellular respiration in the human body.

The efforts of this early research enabled scientists to quantify the calories derived from fats, carbohydrates, proteins and alcohol. This method of measurement was later adapted to measure oxygen consumption, carbon dioxide production and heat production in humans, by having subjects sit or exercise in a large, enclosed, insulated chamber.

Indirect Measurement
Due to the impracticality and limitations of using a big chamber to measure energy expenditure, indirect methods (see Figure 4) were developed to measure a subject’s energy expenditure by determining the amount of oxygen consumed and the amount of carbon dioxide eliminated as air moves in and out of the lungs. Indirect calorimetry, as it’s called, is used widely to measure energy expenditure of exercise in exercise physiology laboratories.

Figure 4.Indirect Calorimetry

This method measures energy expenditure by determining the amount of oxygen consumed and the amount of carbon dioxide eliminated as air moves in and out of the lungs.

Joint Stress With and Without Load

Any weight-bearing activity with repetitive joint movement creates stress on the affected joints, whether the athlete is exercising with or without an additional load. Articular cartilage in knee joints is a lubricated surface that absorbs and transfers the load to allow joint movement without friction.

Moderate joint-loading (30 minutes at 60% of 1-repetition maximum) has been shown to benefit articular cartilage by decreasing markers of inflam-mation (Franciozi et al. 2013). However, excessive exercise, such as competitive ultra-endurance running, can cause articular-cartilage deterioration, similar to that seen in osteoarthritis patients (Helmark et al. 2012).

Exercise professionals should therefore be aware that moderate joint-loading (as in walking) can be beneficial, but extreme overuse can lead to joint harm.

References

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