Final answer:
The individual is improving their strength by lifting heavier weights with fewer repetitions and longer rest periods, which is key in effective strength training. This process requires muscles to continually adapt to heavier loads in order to grow. Individual variability also plays a role in the different results from the same workout program.
Step-by-step explanation:
An individual who performs a low number of repetitions with heavier weights and longer rest periods is improving his or her strength. This approach to exercise falls under the umbrella of effective strength training, where gradually increasing the intensity of the workout is essential to muscle growth and development. To enhance muscle mass, it's not enough to simply continue lifting the same amount of weight; the muscle needs to be challenged with heavier loads over time. This is due to the fact that muscles adapt to the stress placed upon them, and only by increasing this stress with heavier weights can further adaptation and growth be stimulated.
It's also worth noting that different exercise patterns produce different outcomes. For example, a marathon runner, who likely has a higher proportion of slow-twitch muscle fibers, will use a training routine that focuses more on endurance than on heavy lifting and high strength. On the other hand, individual differences, such as natural muscle composition and metabolism, can lead to varied results from the same workout program, as exemplified by a group of twenty people training identically but experiencing different levels of weight loss. These differences in outcomes are a form of individual variability.