We all know a little exercise is good for us; it helps us lose weight and reduces our risk of diseases, such as dementia. Given the overwhelming benefits of exercise, it's clear we should be physically active if we want to live a healthy life. So, more exercise must be better for us, right? Sometimes you can go overboard, but your body will let you know when enough is enough.

Currently, the Centers for Disease Control and Prevention recommends adults get at least 150 minutes per week of moderate physical activity, or 75 minutes per week of vigorous physical activity. Although the guidelines note high-intensity workouts may increase the risk of injuries and heart issues, there's no explicit warning that overtraining can be dangerous to one's health.

Previous research has found chronic training for events such as marathons, ultramarathons, Ironman distance triathlons, and very long-distance bicycle races can lead to negative cardiovascular effects. For example, in a group of patients diagnosed with coronary artery disease, those who exercised beyond the recommended 60-minute maximum experienced a decrease in their antioxidant levels, and stiffening of their blood vessels. Meanwhile, those who exercised 60 minutes or less saw a reduction in free radicals, in addition to improved circulation.

Watch out for these five different signs you're training too hard.

Heart Rate Changes

There are types of molecular changes that can take place in the hearts of athletes that cause certain heart-related health issues. Research has found a very high rate of myocardial fibrosis among lifelong endurance athletes, specifically the hardening of heart cells. This hardening could precipitate sudden cardiac arrest, or induce an irregular heartbeat. Runners who consistently surpass 25 weekly miles have a risk of death comparable to those who don’t exercise.

Musculoskeletal Changes

Muscles and bones inevitably experience damage during exercise and tend to require 24 to 48 hours of rest between workouts for adequate recovery. Muscle fatigue that lasts longer than that means the individual’s physiology has been excessively challenged, and this means that the muscles and energy stores are not recovering effectively. Chronic fatigue after excessive exercise suggests that the individual may be overtraining, according to John Hopkins Medicine.

Immune System Changes

Excessive exercising can compromise our immune system as the body struggles with fatigue and inadequate muscle recovery. Research shows more than 90 minutes of high-intensity endurance exercise can make athletes susceptible to illness for up to 72 hours after the exercise session. Intense exercise can temporarily decrease immune system function.

Hormonal Changes

Over-training influences hormone secretion. Athletes can experience an increased secretion of cortisol and adrenaline — known as stress hormones — that can raise blood pressure and cholesterol levels, which leads to the suppression of the immune system. Over-training can suppress your appetite by increasing the secretion of two hormones — epinephrine and norepinephrine. Inadequate caloric intake can reduce recovery rate and intensify the symptoms of overtraining.

Sleep Changes

Physically pushing ourselves, and the stress the workouts puts on our body, can lead to the rise of cortisol levels. High levels of cortisol and other hormones can influence our sleeping habits. Our cortisol function determines our sleep patterns, so if cortisol is excessively elevated at bedtime, this will prevent the likelihood of getting quality sleep.