11.7: Athletic Performance
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Athletes are useful examples in explaining anaerobic and aerobic energy production, because in their training and competition they attempt to push ATP production to its limits. Athletic events can be roughly divided into two groups, based on whether the fuel used in the event is mainly fatty acids (endurance events) or glucose (strength-and-power events) (see Table 11-1).
Endurance athletes need a steady production of ATP over a long period of time, and they need more ATP than glycogen stores can provide. After about 30-60 minutes of exercise they begin to rely increasingly on fat stores, and use fatty acids as their primary fuel—through aerobic metabolism. Even the leanest endurance athlete has more than enough body fat to fuel an event like a marathon.
| Anaerobic | Aerobic | |
|---|---|---|
| Uses oxygen? | No | Yes |
| Primary fuel | Glucose | Fatty acids |
| Type of exercise | Strength/power | Endurance |
| Cell-type with most capacity | Fast-twitch | Slow-twitch |
Table 11-1: Two types of Energy-Releasing Reactions.
In contrast, strength-and-power athletes (e.g., weightlifters, shot putters, gymnasts, sprinters) use ATP generated mainly from the anaerobic metabolism of glucose (glycolysis) to fuel their event. Oxygen isn’t a limiting factor for these athletes. Because their event is short, they can rely on glycolysis, which doesn’t require oxygen.
The main advantage of glycolysis over aerobic metabolism for strength-and-power athletes is that the reactions of glycolysis are much faster. In other words, ATP can be made much faster (for “bursts of energy”) by anaerobic than by aerobic metabolism.
It follows that those athletes having a greater capacity for glycolysis will be more successful in athletic events that call for a short and intense burst of energy. Muscle cells differ in their capacity to use the anaerobic and aerobic energy-releasing reactions.
Muscle cells can be roughly divided into two types—fast-twitch and slow-twitch. Fast-twitch muscle cells have a high capacity for glycolysis (they have greater amounts of the enzymes needed for glycolysis), allowing them to contract (twitch) rapidly.
Quarter horses and greyhounds are bred for speed; muscle cells in their legs are about 95% fast-twitch.
Slow-twitch muscle cells are geared toward the slower, aerobic energy production. They have more fat and mitochondria (the site of aerobic metabolism) than fast-twitch muscle cells. Slow-twitch cells are also rich in myoglobin, which is similar to the hemoglobin in red blood cells. Like hemoglobin, myoglobin carries oxygen.
Most people have fast-twitch and slow-twitch muscle cells in about equal proportion. Studies looking at cell types in the relevant muscles of top athletes, however, show that strength-and-power athletes, like sprinters, have a greater proportion of fast-twitch cells (>70%), whereas endurance athletes, like long-distance runners, have a greater proportion of slow-twitch cells (>70%).
The relative proportion of fast-twitch and slow-twitch cells in a muscle seems to be genetically determined. For athletes intending to break world records, heredity could well be destiny. Training, however, can markedly enhance the aerobic (and possibly the anaerobic) capacity of both types of muscle cells to produce energy.