To find the probability that Max and Ava will get an odd number of push-ups three times in a row when using a spinner with the numbers 1 to 8, we first need to determine the probability of getting an odd number in one spin.
The numbers on the spinner are: \[ 1, 2, 3, 4, 5, 6, 7, 8 \]
From this set, the odd numbers are: \[ 1, 3, 5, 7 \] There are 4 odd numbers.
The total number of outcomes (the numbers on the spinner) is 8.
Thus, the probability of landing on an odd number in one spin is: \[ P(\text{odd}) = \frac{\text{Number of odd outcomes}}{\text{Total outcomes}} = \frac{4}{8} = \frac{1}{2}. \]
Now, we want the probability of obtaining an odd number three times in a row. Since the spins are independent, we can multiply the probabilities:
\[ P(\text{odd three times}) = P(\text{odd}) \times P(\text{odd}) \times P(\text{odd}) = \left( \frac{1}{2} \right) \times \left( \frac{1}{2} \right) \times \left( \frac{1}{2} \right) = \left( \frac{1}{2} \right)^3 = \frac{1}{8}. \]
Therefore, the probability that Max and Ava will have an odd number of push-ups three times in a row is: \[ \boxed{\frac{1}{8}}. \]