When Paul Simon sings "Slip Slidin' Away," he's crooning about the elusive nature of life, love, and good intentions.

Research now confirms that, despite good intentions, it's all too easy to go slip slidin' away from the benefits of your regular exercise routine.

Fortunately, there's a lot you can do to sustain your commitment to move it, not lose it.

Physical activity protects you from cognitive decline while protecting your cardiovascular system, sex life, balance, mood, and blood sugar levels.

That's because it boosts blood flow to the brain and strengthens neural connections; the same ones that weaken as you get older.

Here's why you need to stay with it: A study published in the journal Frontiers in Aging Neuroscience shows that you lose benefits of physical activity if you slip up for a while, even if you're fit.

Researchers had a group of serious athletes ages 50 to 80 hit the couch for 10 days. After measuring their resting cerebral blood flow to the area of the brain that consolidates memory (the hippocampus), they discovered that blood flow declined significantly from day one of rest to day 10.

So keep moving to keep the long-term, brain-boosting benefits of exercise. Here's how to stay active:

1. Get a workout buddy; you'll keep each other motivated.

2. Use an activity monitor; set goals (and alarms to get you up and out), assess daily accomplishments.

3. Mix it up: If you're bored with one activity, switch to another: aerobics, interval walking, swimming, cycling — even ice skating!