Principles of Adaptation and Stress

The human body adapts well when exposed to stress. The term stress, within the context of exercise, is defined as an exertion above the normal, everyday functioning. The specific activities that result in stress vary for each individual and depend on a person’s level of fitness. For example, a secretary who sits at a desk all day may push their cardiorespiratory system to its limits simply by walking up several flights of stairs. For an avid runner, resistance training may expose the runner’s muscles to muscular contractions the athlete is not accustomed to feeling. Although stress is relative to each individual, there are guiding principles in exercise that can help individuals manage how much stress they experience to avoid injury and optimize their body’s capacity to adapt. Knowing a little about these principles provides valuable insights needed for organizing an effective fitness plan.

Progressive Overload

Consider the old saying, “No pain, no gain.” Does exercise really have to be painful, as this adage implies, to be beneficial? Absolutely not. If that were true, exercise would be a lot less enjoyable. Perhaps a better way to relay the same message would be to say that improvements are driven by stress. Physical stress, such as walking at a brisk pace or jogging, places increased stress on the regulatory systems that manage increased heart rate and blood pressure, increased energy production, increased breathing, and even increased sweating for temperature regulation. As these subsequent adaptations occur, the stress previously experienced during the same activity, feels less stressful in future sessions. As a result of the adaptation, more stress must be applied to the system in order to stimulate improvements, a principle known as the progressive overload principle.

For example, a beginning weightlifter performs squats with 10 repetitions at 50 pounds. After 2 weeks of lifting this weight, the lifter notices the 50 pounds feels easier during the lift and afterwards causes less fatigue. The lifter adds 10 pounds and continues with the newly established stress of 60 pounds. The lifter will continue to get stronger until his/her maximum capacity has been reached, or the stress stays the same, at which point the lifter’s strength will simply plateau. This same principle can be applied, not only to gain muscular strength, but also to gain flexibility, muscular endurance, and cardiorespiratory endurance.

Principle of Specificity

The more specific the exercise to individual training goals, the better. While vigorous ballroom dancing will certainly help develop the cardiorespiratory system, it will unlikely improve a person’s 10k time. To improve performance in a 10k, athletes spend the majority of their time training by running, as they will have to do in the actual 10k. Cyclists training for the Tour de France, spend up to six hours a day in the saddle, peddling feverishly. These athletes know the importance of training the way they want their body to adapt. This concept, called the principle of specificity, should be taken into consideration when creating a training plan.

This can be applied to our previously discussed components of fitness. If you are looking to improve your cardiorespiratory fitness so that you can play a full 90-minute soccer game, you need to focus your training program accordingly. Of course when we look at sport-specific types of training, cardiorespiratory fitness will not be the only programming needs of this type of athlete. For something like a soccer player, they will also need to have agility, speed, strength, power, and good reaction time in order to be able to sprint to defend a breakaway forward, react to a ball being shot on goal, or dribble past a defender. Being able to manage overall workload (and the stress associated with that workload) will also be essential in creating a safe and effective program.

Stress, as it relates to exercise, is very specific. There are multiple types of stress. The three main stressors are metabolic stress, force stress, and environmental stress. Keep in mind, the body will adapt based on the type of stress being placed on it.

Metabolic stress results from exercise sessions when the energy systems of the body are taxed. For example, sprinting short distances requires near maximum intensity and requires energy (ATP) to be produced primarily through anaerobic pathways, that is, pathways not requiring oxygen to produce ATP. Anaerobic energy production can only be supported for a very limited time (10 seconds to 2 minutes). However, distance running at steady paces requires aerobic energy production, which can last for hours. As a result, the training strategy for the distance runner must be different than the training plan of a sprinter, so the energy systems will adequately adapt.

Likewise, force stress accounts for the amount of force required during an activity. In weightlifting, significant force production is required to lift heavy loads. The type of muscles being developed, fast-twitch muscle fibers, must be recruited to support the activity. In walking and jogging, the forces being absorbed come from the body weight combined with forward momentum. Slow twitch fibers, which are unable to generate as much force as the fast twitch fibers, are the type of muscle fibers primarily recruited in this activity. Because the force requirements differ, the training strategies must also vary to develop the right kind of musculature.

Environmental stress, such as exercising in the heat, places a tremendous amount of stress on the thermoregulatory systems. As an adaptation to the heat, the amount of sweating increases as does plasma volume, making it much easier to keep the body at a normal temperature during exercise. The only way to adapt is through heat exposure, which can take days to weeks to properly adapt.

In summary, to improve performance, being specific in your training, or training the way you want to adapt, is paramount.

Dawn Markell & Diane Peterson, Health and Fitness for Life. MHCC Library Press. Sept 4, 2019. https://mhcc.pressbooks.pub/hpe295