3.3: Looking for More Work
- Page ID
- 56120
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)If you’re reluctant to eat less, you’ll have to be more active to lose weight. How much more depends on various factors, and it’s important to keep several points in mind when estimating the calories used in different types of activities:
- The energy used in weight-bearing exercises is quite variable. Not only does the caloric output depend on how far you move, but also on how much you weigh (i.e., how much weight is moved). Someone weighing 120 pounds uses about 70 calories walking a mile in 20 minutes, whereas someone weighing 200 pounds uses about 105 calories walking that same mile. (Good reason to carry an infant in a baby carrier—or books in a backpack—if you’re looking to use more calories.)
This also means that as you lose weight, you will use fewer calories for the same walk (unless the infant you are carrying gains what you lose, or you add a counterbalancing number of books to your backpack).
The amount of energy used in walking is affected by other factors as well, including the walking surface (e.g., sand or pavement, uphill, downhill, or flat), distribution of weight on the walker’s body, the walker’s physical fitness. Also, we use fewer calories in an activity as we become better at it. Think of the gracefulness of experienced runners.
- In non-weight-bearing exercise, other physical factors can make a difference in energy output. In swimming, for example, a more buoyant person expends less energy staying on top of the water.
- People vary quite a lot in how much energy they expend in a given activity. Tennis isn’t always tennis. Suppose you are much better than your opponent. You return shots while standing at the net, and your opponent runs a lot. But the next day you are outclassed. Now it’s your turn to run. You hit harder, stretch further, and pant. The third day you play doubles, and one of the partners is a lawyer who frequently stops to dispute line-calls and asks the score after each point. Even in a lecture hall, some people sit at the edge of their seats and fidget. Others are slumped in their seats, barely awake.
Most of us are quick to imagine how we can increase our output of energy. We imagine ourselves deliberately parking a mile away from work, or taking up biking or swimming. But for many of us, such an active imagination doesn’t translate into an active body. This leaves us receptive to claims of painless shortcuts. It’s important to remember that there are no magic exercises, just as there are no magic foods.
Increasing the output of energy is a fairly obvious matter (see Fig. 3-1). Once an appropriate activity is chosen—one which uses a good bit of energy and, ideally, involves moving the whole body over a long distance (e.g., a long walk, or a simulated long walk on a treadmill)—the problem is chiefly one of persistence.
Increasing physical activity is helpful in other ways. What we want to lose is fat, but muscle mass is also lost with dieting. Exercise helps maintain muscle mass, and also is a counterbalance to the drop in basal metabolism triggered by a low-calorie diet. Furthermore, if the exercise leads to more muscle mass, basal calorie needs increase.