By now, you know the drill: For better heart health, exercise is nonnegotiable. To be exact, adults should engage in at least 150 minutes of moderate intensity or 75 minutes of vigorous intensity physical activity each week, according to the American College of Cardiology. But whether you spend your time playing pickup basketball, moving heavy boxes at work or taking daily walks around the neighborhood, you’re helping your heart, right?

Maybe not. A team of international researchers has found that not all exercise is created equal when it comes to cardiovascular fitness. In fact, when it comes to various types of physical activity, significant differences may exist in the cardiovascular benefit—some may even do more harm than good.

Study details: The researchers started with data from an ongoing study that has been collecting the health records of about 10,000 participants (ages 50 to 75) for 10 years. The data included self-reports about the frequency, duration and intensity of their physical activity while engaging in a sport (such as soccer or tennis), while at work (for example, digging ditches or carrying heavy buckets) and during their leisure time (such as gardening or outdoor walks).

“Our idea was to look at whether all types of physical activity are beneficial, or whether under some circumstances physical activity can be harmful,” explained lead study author Jean-Philippe Empana, MD, PhD, research director of the French National Institute for Health and Medical Research in Paris.

To assess the cardiovascular health of the participants, the researchers performed a sophisticated form of ultrasound of the carotid artery. This imaging allowed the team to measure “baroreflex sensitivity”—a medical term for the body’s reaction to sudden, potentially harmful changes in blood pressure.

The results: When the team put it all together, the analysis showed that physical sports activity was associated with a healthy baroreflex. On the other hand, in study participants who performed regular physical occupational activity (such as carrying heavy loads), the baroreflex result was linked to arterial stiffness, which may lead to heart rhythm disorders and other cardiovascular dangers. The leisure activities did not appear to have a dangerous effect.

In summarizing the results, the authors warned against overstating the findings. “They do not suggest that movement at work is harmful for health,” said Dr. Empana, “instead they suggest that chronic, strenuous activity (such as lifting heavy loads) at work may be harmful.”

The authors now want to expand on these findings to further study how physical activity in the workplace affects health.

Takeaway: If your job requires you to do physically taxing, repetitive work, talk to your doctor about other ways to minimize your risk for heart disease.