There's no longer any doubt that exercise can be a serious mood booster for people with major depressive disorder. Even an hour of physical activity a week can be enough to reduce the risk of future episodes.

Surprisingly, little is known about the more immediate effects of exercise on specific characteristics of both mood and mind among people with depression, both during an exercise session and straight after.

"A lot of previous research on the effects of exercise on mental health, in general, have used very broad measures of wellbeing," says Iowa State University kinesiologist Jacob Meyer.

"What we were interested in, specifically, is: how does acute exercise – that is, one session of exercise in a day – influence the primary symptoms of depression."

Chronic forms of depression consist of a variety of mental changes that make it more than just a feeling of glumness. For many, there's the sheer loss of enjoyment and pleasure that comes with depressive episodes – a symptom referred to as anhedonia.

Then there's the disorder's relationship with impaired cognitive functions, including memory loss and processing speed, which may also benefit from exercise.

To add detail to our knowledge of how a workout influences changes in both mood and mental skills, Meyer and colleagues analyzed various test scores of 30 volunteers before, during, and after either a moderately intense half-hour cycling session, or a session of quiet rest.

Tests included a questionnaire to evaluate current mood and feelings, a scale to measure anhedonia, and several cognitive assessments, including something called a Stroop color and word test.

Taken together, the evaluations were intended to form a clearer profile of how a person's mental state evolves throughout an exercise session while they're dealing with depression.

Mid-cycle, participants generally experienced an improvement in their mood, one that persisted for at least 75 minutes after the workout had ended.

Feelings of anhedonia had also lifted, though were starting to creep back 75 minutes post-workout. However, compared with those who'd quietly rested, it was still a positive result.

Perhaps more surprising were the variations in cognitive ability. In contrast with previous findings on healthy individuals, which predicted overall improved reaction times, the results among this sample were mixed.

During exercise, participants' Stroop test results were slightly faster. Yet this dropped 25 and 50 minutes after they'd stopped, becoming slower than those who hadn't exercised.

It's not clear why this might be the case, or whether it's linked with other major depressive disorder symptoms at all.

The fact there's an immediate improvement to mood and general enjoyment after physical activity helps build a case for people with depression that just might encourage them to exercise more.

That said, it might also not be that simple. Depression saps motivation, meaning even anticipation of the buzz that comes with getting out of the house and moving might not be enough to drive a change in habit.

Still, for those who do manage to take the critical step, knowing there's a window of at least an hour where the dark cloud lifts could help plan out the day a bit better.

"The cool thing is these benefits to depressed mood state and anhedonia could last beyond 75 minutes," says Meyer.

"We would need to do a longer study to determine when they start to wane, but the results suggest a window of time post-exercise when it may be easier or more effective for someone with depression to do something psychologically or cognitively demanding."

This research was published in Psychology of Sport and Exercise.