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Chapter 1: Problem 88

ATHLETICS: Cardiovascular Zone Your maximum heart rate (in beats per minute) may be estimated as 220 minus your age. For maximum cardiovascular effect, many trainers recommend raising your heart rate to between \(50 \%\) and \(70 \%\) of this maximum rate (called the cardio zone). a. Write a linear function to represent this upper limit as a function of \(x\), your age. Then write a similar linear function to represent the lower limit. Use decimals instead of percents. b. Use your functions to find the upper and lower cardio limits for a 20 -year-old person. Find the cardio limits for a 60 -year-old person.

Short Answer

Expert verified
For a 20-year-old, cardio limits are 100 bpm (lower) and 140 bpm (upper); for a 60-year-old, 80 bpm (lower) and 112 bpm (upper).

Step by step solution

01

Determine Maximum Heart Rate Function

The maximum heart rate (MHR) can be expressed as a function of age \(x\) using the formula: \( MHR(x) = 220 - x \). This function provides the estimated maximum heart rate for a given age \(x\).
02

Define Upper Limit Function

The upper limit of the cardio zone is \(70\%\) of the maximum heart rate. To express this as a linear function of age \(x\), multiply the maximum heart rate function by 0.7: \( Upper(x) = 0.7 \times (220 - x) \).
03

Define Lower Limit Function

The lower limit of the cardio zone is \(50\%\) of the maximum heart rate. Formulate this linear function by multiplying the maximum heart rate function by 0.5: \( Lower(x) = 0.5 \times (220 - x) \).
04

Compute Cardio Limits for a 20-Year-Old

For \(x = 20\), calculate the upper and lower limits. Substitute \(x = 20\) into the functions:First, calculate the upper limit: \( Upper(20) = 0.7 \times (220 - 20) = 0.7 \times 200 = 140 \).Next, calculate the lower limit: \( Lower(20) = 0.5 \times (220 - 20) = 0.5 \times 200 = 100 \).The cardio limits for a 20-year-old are 100 bpm for the lower limit and 140 bpm for the upper limit.
05

Compute Cardio Limits for a 60-Year-Old

For \(x = 60\), calculate the upper and lower limits. Substitute \(x = 60\) into the functions:First, calculate the upper limit: \( Upper(60) = 0.7 \times (220 - 60) = 0.7 \times 160 = 112 \).Next, calculate the lower limit: \( Lower(60) = 0.5 \times (220 - 60) = 0.5 \times 160 = 80 \).The cardio limits for a 60-year-old are 80 bpm for the lower limit and 112 bpm for the upper limit.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Maximum Heart Rate
The concept of maximum heart rate is quite straightforward. It is the highest number of times your heart is capable of beating in one minute during maximum physical exertion. Understanding your maximum heart rate is essential for setting fitness goals and tracking your cardiovascular health. To estimate your maximum heart rate, you can use a simple formula:
  • Subtract your age from 220. This gives the estimated maximum beats per minute (bpm) that your heart can achieve.
For example, if you are 30 years old, your maximum heart rate would be calculated as follows: \[ MHR = 220 - 30 = 190 \] bpm. This means that theoretically, your heart shouldn't exceed 190 beats per minute during intense exercise. It's a widely used method because of its simplicity and reasonably accurate prediction for most people.
Cardio Zone
The cardio zone refers to a range of heart rates that optimizes your cardiovascular training during exercise. This zone is determined as a percentage of your maximum heart rate and is a sweet spot for improving heart health and overall fitness without overstraining your body. For effective cardio training, it is generally recommended to maintain a heart rate between 50% and 70% of your maximum heart rate.

To find your cardio zone, calculate:
  • The lower cardio limit by multiplying your maximum heart rate by 0.5 (50%).
  • The upper cardio limit by multiplying your maximum heart rate by 0.7 (70%).
For instance, using the maximum heart rate of 190 bpm from the previous example, the cardio zone can be calculated as:
  • Lower limit: \[ 0.5 \times 190 = 95 \] bpm
  • Upper limit: \[ 0.7 \times 190 = 133 \] bpm
Thus, for optimal cardiovascular fitness, aim to maintain your heart rate between 95 and 133 bpm during exercise.
Age-Related Calculations
Age plays a crucial role in determining both the maximum heart rate and the cardio zone. The reason is that as you age, your maximum heart rate typically decreases. This relationship is represented through a linear function, which follows the formula mentioned earlier: \[ MHR(x) = 220 - x \] where \(x\) is your age. This simple subtraction provides a guideline for healthy maximum exertion levels as you grow older. Moreover, the calculated cardio limits, both upper and lower, leverage these age-related calculations to ensure that your fitness regime is tailored to your physiological needs.By understanding and applying age-related adjustments, you can formulate a more effective and personalized exercise plan. This knowledge ensures that your workouts remain safe and efficient, helping you maintain cardiovascular health through different stages of life.

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Most popular questions from this chapter

Find, rounding to five decimal places: a. \(\left(1+\frac{1}{100}\right)^{100}\) b. \(\left(1+\frac{1}{10,000}\right)^{10,000}\) c. \(\left(1+\frac{1}{1,000,000}\right)^{1,000,000}\) d. Do the resulting numbers seem to be approaching a limiting value? Estimate the limiting value to five decimal places. The number that you have approximated is denoted \(e\), and will be used extensively in Chapter 4 .

BUSINESS: Cost Functions A lumberyard will deliver wood for \(\$ 4\) per board foot plus a delivery charge of \(\$ 20\). Find a function \(C(x)\) for the cost of having \(x\) board feet of lumber delivered.

Explain why, if a quadratic function has two \(x\) intercepts, the \(x\) -coordinate of the vertex will be halfway between them.

$$ \text { If } f(x)=a x, \text { then } f(f(x))=? $$

BUSINESS: Straight-Line Depreciation Straight-line depreciation is a method for estimating the value of an asset (such as a piece of machinery) as it loses value ( \({ }^{\prime \prime}\) depreciates" \()\) through use. Given the original price of an asset, its useful lifetime, and its scrap value (its value at the end of its useful lifetime), the value of the asset after \(t\) years is given by the formula: $$ \begin{aligned} \text { Value }=(\text { Price })-&\left(\frac{(\text { Price })-(\text { Scrap value })}{(\text { Useful lifetime })}\right) \cdot t \\ & \text { for } 0 \leq t \leq(\text { Useful lifetime }) \end{aligned} $$ a. A newspaper buys a printing press for $$\$ 800,000$$ and estimates its useful life to be 20 years, after which its scrap value will be $$\$ 60,000$$. Use the formula above Exercise 63 to find a formula for the value \(V\) of the press after \(t\) years, for \(0 \leq t \leq 20\) b. Use your formula to find the value of the press after 10 years. c. Graph the function found in part (a) on a graphing calculator on the window \([0,20]\) by \([0,800,000] .\) [Hint: Use \(x\) instead of \(t\).]
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