We've written before about how it doesn't always take long stints of exercise to reap the health benefits.

Now a new study has backed this up. After looking at the exercise habits of 577,909 adults in the US, researchers have found that just 10 minutes of regular aerobic exercise (or "cardio") a week can substantially cut the risk of death from flu or pneumonia.

When it comes to moderate-to-vigorous physical activity (MVPA), the recommended level is at least 150 minutes per week of moderate-intensity activities (like brisk walking), or 75 minutes per week of vigorous-intensity activities (like cycling).

But the reality is that many of us don't get close to that. So the latest study – led by a team from the Centers for Disease Control and Prevention in Georgia and the Brooke Army Medical Center in Texas offers some good news for those of us trying to squeeze in small bursts of activity in our week.

"The risk was significantly lower among participants who performed 10–150 min/week of leisure-time MVPA, compared with those who performed none," write the researchers in their published paper.

"Although this level is often labeled 'insufficient' because it falls below the recommended duration, it may confer health benefits relative to physical inactivity."

The relative risk of dying from flu or pneumonia dropped by 21 percent on average in this 10-150 weekly minutes group, compared with those who did no exercise at all, based on 20 years of data. In other words, some activity is better than none.

Logging 150-300 and 301-600 minutes per week of MVPA was associated with 41 percent and 50 percent reductions in risk, compared with no activity at all. However, no extra benefits were seen past 600 minutes per week, suggesting a plateauing effect.

The team also looked at muscle-strengthening activity (MSA): the recommended weekly amount for this is at least two sessions per week. Taken with MVPA, those who met both targets averaged a 48 percent reduction in risk of death from flu or pneumonia, compared with those who met neither target.

With MSA in isolation, there was a J shape, with a drop in flu and pneumonia death risk to begin with, and then a rise as the sessions increased. While the study didn't examine this in detail, one explanation is that frequent, vigorous MSA can have a detrimental effect in terms of blood pressure and blood flow.

"Independent of achieving the aerobic guideline, adults who performed 2 MSA episodes/week had lower mortality than those who performed fewer than 2 episodes, while mortality was higher among those who performed 7 or more episodes," write the researchers.

Despite the large sample size, the study has its limitations – not least that it's based on surveys filled out by the participants, not direct observations. The study doesn't show a direct causal relationship either, but rather hints at a link between exercise and the risk of dying from influenza or pneumonia, which can be weighed up alongside other research.

What the findings do show is a lot of variation in how well people keep to the recommended weekly guidelines for exercise, based on a host of factors – including age, sex, BMI category, and other health conditions.

Half of the study participants, 50.5 percent, didn't meet the weekly target for either MVPA or MSA. The key takeaways to remember from this particular piece of research are that we need to do more to get more people active – and that even a few minutes of exercise across a week could make a big difference.

"Considering the plausible biological mechanisms and the consistency with previous studies, this protective association may warrant additional clinical and public health efforts to decrease the prevalence of aerobic inactivity and inadequate MSA," write the researchers.

The research has been published in the British Journal of Sports Medicine.