Sorry, folks. This is it. If new research is correct, this could be the best it's going to get for humanity in terms of physical fitness. According to the paper, humans have biological limitations - and there may be no more improvements for the species.

And it's partially our own fault. Our effect on the environment, including pollution and climate change, is having a negative impact on our biological limits.

A multi-disciplinary team led by physician Jean-Fran├žois Toussaint from Paris Descartes University has conducted a review of over 160 studies stretching back 120 years. This research looked into longevity, how well humans can perform athletically, height trends over time, and the environment.

What the review has concluded is that lifespan, physical performance, and height - which were steadily rising throughout the 20th century - have plateaued over the last three decades, since around 1980.

"These traits no longer increase, despite further continuous nutritional, medical, and scientific progress," Toussaint said. "This suggests that modern societies have allowed our species to reach its limits."

This review, the researchers note in their paper, is only possible now. Reliable medical and sports records, and the ability to accurately measure things like physical performance have became available only during the last century - and only now, when we have over a century's worth of these records, can we look at them all together to observe trends.

The effects of the plateau are expected to manifest in more people reaching the threshold, but fewer records being broken; fewer people exceeding the previous record lifespan, fewer people breaking sports records.

We may already be seeing these effects. No one has yet lived older than Jeanne Calment, who died in 1997 aged 122 years and 164 days. No one has yet beaten sprinting records for 100 metres and 200 metres set by athlete Usain Bolt in 2008.

We may still see average health and height statistics rise, but in some places in Africa, the researchers note, average heights have begun to decline, indicating insufficient nutrition.

And environmental pollution has been linked to low birth weight, poor health, and lower life expectancy. Climate change has also been linked to lower life expectancy, and the spread of diseases such as malaria.

These factors may contribute towards preventing humans from reaching the upper limits of fitness and lifespan.

"Observing decreasing tendencies may provide an early signal that something has changed but not for the better," Toussaint said.

"The current declines in human capacities we can see today are a sign that environmental changes, including climate, are already contributing to the increasing constraints we now have to consider."

But, he notes optimistically, now that we have some idea about what our upper limits are if this analysis is correct, governments around the world can try to work towards reaching the highest possible values for their populations.

"With escalating environmental constraints, this may cost increasingly more energy and investment in order to balance the rising ecosystem pressures. However, if successful, we then should observe an incremental rise in mean values of height, lifespan and most human biomarkers," he said.

The paper was published in the journal Frontiers in Physiology.