When it Comes to Overtraining in Athletes, Less May be More

High-performing athletes are some of the most motivated, energetic and focused people on the planet. They push their body to the limit, day in and day out, constantly striving to reach that next level. But what happens to the human body at that fine line between optimal training and overtraining?

Moderate overtraining, also known as overreaching, is a well-recognized phenomenon in the sporting world, occurring when athletes push their body beyond its capacity to recover for an extended period of time, leading to fatigue, lower exercising heart rate, increased incidence of illness and reduced athletic performance. Overtraining is most commonly seen during challenging training blocks and training camps, and can occur across all high-intensity sports.

Researchers in the Department of Human Health and Nutritional Sciences have pooled their expertise to identify the mechanism behind the negative effects of overload training. The study was led by Alexandra Coates, a previous elite triathlete turned coach and MSc student,  who worked alongside Prof. Jamie Burr, her supervisor in the Human Performance and Health Research Lab, as well as Prof. Philip Millar, head of the Clinical Cardiovascular Physiology Lab.

“I feel like I have an edge because I’ve experienced it and I work with these athletes all the time, so it’s not just the science, I know how to apply it,” explains Coates.

Coates and her colleagues hypothesized that some of the negative effects of overtraining are caused by decreased cardiac output due to arterial stiffness. Arteries are a type of blood vessel that carry blood away from the heart to provide the rest of the body with oxygen. This is especially important for athletes, whose muscles are working overtime during exercise. When arteries are flexible and relaxed, they can easily handle changes in blood flow being pumped out by the heart. When arteries become stiff, the heart has to work significantly harder to push high volumes of blood through the vessels and to the rest of the body. This is what led Coates to wonder if the effects of overtraining were linked to arterial stiffness, a hypothesis that had never been tested in the literature.

To address her research question, Coates recruited a group of triathletes and cyclists to participate in either a control or over-training program. Both groups continued their base training program, while the overtraining group conducted three additional, challenging workouts each week for three consecutive weeks. Coates found it takes a lot to over-train these extremely fit athletes, but she crafted the perfect combination of workouts to ensure they reached exhaustion, even though it may have led to some serious sweat and tears for the athletes. The first overtraining workout involved four 30-second repeats of anaerobic, high-resistance cycling, which Coates describes as “the longest 30 seconds of your life”. The second workout was a 15 km hilly time trial on a stationary bike, and the third was a 2-hour weekend cycle which Coates monitored via Polar heartrate watches. To add a little extra kick to each individual’s workout, Coates played on their competitive nature and kept a scoreboard for the fastest female and male times for each workout.

“This research is pretty cool because you meet a lot of crazy people who are willing to push themselves extremely hard. I had 17 people in the overtraining group, and nobody dropped out!” exclaims Coates.

Following three weeks of either regular or overtraining exercise, Coates measured a variety of health indicators, including pulse wave velocity. This technique measures how quickly a pulse moves from one location to another within a blood vessel, which indicates the level of arterial stiffness. Coates discovered that, compared to the regular training group, the overtrained athletes consistently showed an increased pulse wave velocity, revealing an increase in arterial stiffness following periods of overtraining.

The findings support Coates’ hypothesis and implicate arterial stiffness in the performance deficits experienced by athletes during periods of overtraining, which means that exercise physiologists can now start looking at ways to mitigate these impacts and optimize training programs.

Coates is now pursuing a PhD within the Human Performance and Health Research Lab, where she continues to study cardiac function in high performing athletes.  She recently spent time at the University of Liverpool to learn more about cardiac ultrasound, and intends to use the technique to monitor cardiac output during exercise in even greater detail. Using echocardiograms during exercise comes with many challenges, but as a hard-working athlete herself, Coates has the work-ethic and motivation to continue producing exciting research.

“The best part of the research is just seeing what the human body can actually do. It can always do so much more than you would expect.”

This research was funded by a grant from the Natural Science and Engineering Research Council of Canada,the Ontario Research Fund,  and the Canada Foundation for Innovation.

Read the full study in the Medicine & Science in Sports & Exercise.

Read about other CBS Research Highlights.