Hiking trails are good for more than a challenging outdoor walk. The uneven terrain forces the body to use more stabilizing muscles in the abdominals and back, which improves balance and strengthens the core. Sprints or walking fast uphill puts you into an anaerobic zone, which taxes the muscles and benefits the cardiovascular system.

Los Angeles Times staffers took to some trails in the San Gabriel Mountains near Los Angeles with Keli Roberts (www. keliroberts.com), trainer and former IDEA Health & Fitness Association international instructor of the year. The exercises she demonstrated are perfectly suited to any basic hiking trail, such as those at Clinton Lake State Park in south Lawrence. Although beginners can tackle these moves, it’s important to pay attention to the modifications and make sure the terrain isn’t excessively rocky or craggy, because it’s easy to slip on loose rocks and dirt. Always keep an eye on the ground while moving. And stay focused on the task at hand. Take in the view on a break, not during an exercise that requires concentration.

First, warm up: Walk briskly, run or run-walk for 15 minutes, increasing speed as you go.

Here are some exercises to take on the trails to pump up your workout:

Uphill walking lunges: Take walking lunges out of the gym and put them on a hill, and suddenly this already challenging exercise becomes super-tough. “It’s a complete exercise for the lower body” that targets hamstrings, quads, glutes and inner thighs, Los Angeles trainer Keli Roberts says. It conditions the ankles and feet when the body tries to right itself on an uneven surface.

In the lunge position, keep knees at a 90-degree angle, and don’t rush the movement — take a second or two to stabilize the body before pushing off. Pumping the arms helps engage more core muscles.

How many: One to three sets of 20 paces each with a one- to two-minute rest between sets.

Hill sprints: Repeated sprints uphill followed by rest periods improve cardio function and work the leg muscles. Choose a navigable path about 50 meters (164 feet) long from the flat to the crest of the hill. Go for maximum speed, pumping the arms as you go. Walk down the hill to recover completely, about two minutes, before sprinting again. Once you feel yourself flagging during the run, stop. This is about quality, Roberts says, not quantity.

How many: Varies depending on ability, but no more than 10.

Incline push-ups: These are easier than regular push-ups but still provide good upper-body conditioning. Find a sloping wall or embankment and place both hands on the wall at shoulder height. Lower your chest toward your hands, keeping elbows out and the body in alignment from head to toe — don’t push hips out, or stomach in. This move works triceps, upper back, shoulder and chest muscles, and abdominals. Lifting one leg during the movement destabilizes the body, engaging more of the core.

How many: Two sets of eight to 15 reps. (Try alternating with sets of walking lunges.)

Double-leg stretch

This core-strengthening move borrows from Pilates and can be done on top of a picnic table, flat bench or flat rock. Begin by lying face up, arms and legs tucked in toward the torso. Extend arms and legs out at the same time, keeping them off the table — the lower they are, the tougher this exercise becomes. Exhale on the extension, then inhale as the arms and legs are brought in. The head and neck are lifted but not strained — beginners can keep their head on the table. The trunk is held still during the movement, and all core muscles in the abdomen and back are engaged.

How many: One to two sets of 10 to 15 reps.

Interval runs, or fartleks

Don’t giggle. Fartlek is Swedish for “speed play” and refers to alternating short periods of high- and low-intensity aerobic conditioning, without a break, to improve the cardiovascular system. Roberts recommends switching between one minute of fast running followed by one minute of slow running or even walking (beginners can alternate between fast and slow bouts of walking). “This is a great drill that makes you a much faster runner,” she says. On the downhills, Roberts suggests trying to keep the same pace,