Injury rehab: your boots are made for walking!

Walking and gradient

The amount of energy (and therefore the oxygen demand) required for walking is not just a function of walking speed – it also depends on the gradient. That leisurely 3mph stroll on the flat soon turns into a hard slog up a 1 in 5 or 20% gradient. Runners can use this fact to boost the intensity of a walking workout to elevate heart rates enough to ensure the workout delivers aerobic benefits. Take an 80kg adult for example; table 1 below shows the impact that adding gradient into a walking workout can have on the calorie per hour burn rate(6).

To give you feel for these figures, an adult of any weight walking at 4mph up a 1 in 6 hill raises their metabolism to around 13 METS – ie the calorie burn rate and oxygen consumption is 13 times higher than at rest. That’s a fairly challenging workout; a well-conditioned endurance athlete with a maximum oxygen uptake of over 60mls.kg-1.min-1 walking at this speed and gradient would have to work at nearly 70% of their VO2max to stay with the pace!

Table 1: The effect of gradient on walking energy expenditure (kcals per hour)

Walking and terrain

It’s not just gradient and speed that affect the energy demand during walking. Get off a tarmac road or pavement, and for any given speed and gradient, energy output rises dramatically. Table 2 below gives correction factors for different terrains(7). Multiplying the speed/gradient figure by the correction factor gives you an indication of how much energy you’d need to maintain your speed up the same gradient over different terrain. For example, walking at 4mph on a flat smooth surface such as pavement burns 400cals per hour (for an 80kg adult). For the same speed over a flat ploughed field, the energy requirement would rise to 1.5 x 400 = 600cals per hour.

Table 2: the effect of terrain on walking energy expenditure*

* data from Richmond, Potter and Santee: ‘Terrain factors for predicting walking and load carriage energy costs: review and refinement’ J. Sport Hum. Perform., 3 (3) (2015), pp. 1-26

In fact, even small changes in surface can have a significant impact on energy expenditure while walking. In a 2021 study by the US Department of Defense and US National Institutes of Health, researchers investigated and compared the impact of terrain type on energy expenditure when walking on sidewalks, dirt, gravel, grass, and woodchips(8). The results showed that walking on a flat surface of woodchips at 2.8mph required 27% more energy expenditure than walking on the sidewalk at the same speed (see figure 1).

Figure 1: Energy costs and net metabolic rate when walking on different surfaces

Cumulative energy costs of walking

One of the main battles for runners suffering an extended layoff due to injury is weight management. Significant weight gain not only makes restarting training harder, it also increases the risk of a subsequent injury(9). Any alternative activity during a layoff period should therefore be one that increases energy burn sufficiently to minimize weight gain. Many people assume that walking doesn’t really burn up that many calories but table 3 below shows how body weight and walking speed influence energy expenditure. Compare the ‘calories per hour’ figures for brisk walking (4-5mph) to other sports and fitness activities and you begin to see that walking can actually be a quite effective form of aerobic exercise, especially if performed on hillier or rougher terrain!

Table 3: Body weight and energy costs of walking in calories per hour

Walking compared to other activities

It’s tempting to think of walking as too gentle to count as ‘real’ exercise, but how does it actually stack up compared to other sports and activities? All the figures given below are the energy costs in calories per hour for a mythical 12-stone adult. You can see below that even walking on the flat is respectably energetic, being more energy intense than sports such as weight training and gymnastics. Add in a bit of gradient or challenging terrain however and the intensity skyrockets!

Practical applications

In terms of the physiological demands, the data is clear: with the right gradients and terrain, walking can provide the necessary physiological stimulus to help maintain cardiovascular fitness (or at least minimize losses), and a sufficient calorie burn to help stave off weight gain. Even better, the overlap between walking and running muscle recruitment patterns means that there is a significant transfer of training effect, but without the harsh impact or loading that might interfere with the healing and recovery process. Despite the above however, caution is still required; having suffered a painful knee injury, you wouldn’t want to (or even be able to) head out to walk the hills the next day. Here then are some practical tips for injured runners, but bear in mind, they are generalized recommendations. You should always seek help from a qualified physiotherapist for more specific advice:

• When injury occurs, the first phase of recovery should always be rest until the immediate pain subsides. Regular icing and the use of anti-inflammatories such as Ibuprofen may help in the early stages.
• Once the initial pain has settled, and you can walk around the house with little or no discomfort, you can think about commencing some walking.
• Just as you would with running, start by walking slowly on the flat, and only for very short distances (5-10 minutes) to see how you feel the next day. You can then begin to increase the distance and speed. But only if you remain pain free.
• Walk on the flat to begin with and only introduce some gradient once you have a good few flat sessions under your belt. Start with mild inclines and only progress to steeper inclines if you remain completely pain free. Although still gentle overall, walking uphill will impose significantly more physiological demands on healing tendons, ligaments and muscles.
• Once you can cope okay with gradients, you can try introducing some different terrains. Start with something fairly undemanding – eg woodchip trails. Assuming all is okay, you can move onto sand and eventually much more uneven ground such as grassy rutted fields and rocky paths. Introduce these surfaces with caution however as more uneven terrains will impose far greater lateral and twisting forces on the lower limb joints, muscles and tendons.
• Provided you remain pain free, you can think about higher-intensity workouts using much steep gradients combined with a brisk pace to drive up intensity. These are best performed on smoother terrains however as descending downhill across very uneven terrain is hard going for recovering joints and muscles.
• Wear comfortable and supportive shoes or boots for your walking; your existing running shoes are probably okay for walking sessions on tarmac – unless they are implicated in the aetiology of your injury in the first place.

References

1.       Am J Sports Med. 2018 Jul;46(9):2211-2221

2.       PLoS One. 2023 Aug 17;18(8):e0288814. doi: 10.1371/journal.pone.0288814. eCollection 2023

3.       Clin Biomech (Bristol, Avon). 1996 Jul;11(5):253-259. doi: 10.1016/0268-0033(95)00068-2

4.       Am J Sports Med. 2021 Jul;49(8):2227-2237

5.       Instr Course Lect. 1995;44:497-506

6.       McArdle Katch & Katch ’Exercise Physiology: Nutrition, Energy, and Human Performance’ – 8th edition. Wolters Kluwer Publishing 2014

7.       J. Sport Hum. Perform., 3 (3) (2015), pp. 1-26

8.       PLoS One. 2021; 16(1): e0228682

9.       BMJ Open. 2019 Sep 6;9(9):e032627