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Chapter 12. Importance and Derivation of Aerobic Capacity

A 45-year-old male patient (82 kg) has a peak exercise capacity of 10 METs. He breaks both femurs in a motor vehicle accident, and two leg casts are placed on him for 8 weeks. After the leg casts are removed, he begins rehabilitation therapy. Two weeks later, his V̇O2max is again 8 METs. Which variable in the Fick equation is most responsible for the patient's decreased aerobic fitness?

a. Decreased stroke volume at maximal exercise

b. Increased heart rate at maximal exercise

c. Decreased O2 extraction at maximal exercise

d. Increased O2 extraction at maximal exercise

e. Decreased heart rate at maximal exercise

The most correct answer is b.

A decrease in stroke volume at maximal exercise is the most consistent finding during bed rest and other forms of detraining. Consult Table 12.3 and Figs. 12.3 and 12.4 for more specifics based upon age and gender.

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Table 12.3. Age, gender, and training effects on the Fick equation in maximal exercise
Parameter Sedentary men Trained men Sedentary women Trained women
Age Group (yrs) 23-31 58-68 21-31 59-72 20-27 60-72 18-30 51-63
Height (cm) 177 (8) 177 (6) 180 (5) 173 (6) 165 (7)b 165 (8)b 167 (6) 165 (6)
Weight (kg) 75 (12) 83 (12) 68 (12) 66 (7) 58 (9)b 67 (15)b 55 (7) 59 (6)
Body fat (%) 17 (7) 29 (6)a 9 (3) 18 (4)a 22 (7) 36 (6)ab 17 (5) 25 (6)
O2max (L/min) 3.4 (.4) 2.2 (.3)a 4.4 (.5) 3.1 (.4)a 2.1 (.4) 1.5 (.2) 2.9 (.4)b 2.1 (.2)ab
O2max (mL/kg/min) 46 (6) 27 (5)a 64 (4) 48 (4)a 37 (4) 22 (3)ab 52 (3)b 35 (4)ab
O2max (mL/kg fat-free mass/min) 55 (6) 38 (5)a 70 (5) 58 (6)a 47 (5)b 35 (3)a 63 (5)b 49 (4)b
Q̇max (L/min) 21 (2) 16 (3)a 27 (3) 21 (2)a 15 (3) 12 (2)ab 18 (2)b 14 (2)ab
HRmax (beats/min) 185 (9) 163 (15)a 178 (6) 165 (9)a 189 (5) 162 (10)a 181 (9) 167 (9)a
SVmax (mL/beat) 115 (16) 101 (19) 154 (20) 124 (14)a 80 (12) 74 (8)b 102 (12)b 85 (9)#
CaO2 - CO2 (mL/dL) 15 (1) 14 (1)a 16 (1) 15 (1) 14 (1) 12 (2)b 15 (1) 14 (1)

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