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