Skipping may be easier on the knees than running and burn more calories

(Reuters Health) - Skipping - an exercise many people may not have tried since their school days on the playground - may actually be a great grownup workout because it puts less stress on the knees than running while burning more calories, a recent study suggests.

Despite the many health benefits of running, the number of running-related injuries is on the rise and as many as 79 percent of runners report injuries in any given year, researchers note in Gait & Posture. Injuries to the knees and lower extremities are common because running mechanics produce large amounts of force on the body with every stride - and because runners often develop repetitive stress injuries by allowing insufficient recovery time.

For the current study, researchers compared the contact force on the knee for 20 healthy, young adults when they ran and skipped at the same speed.

Compared to skipping, running produced almost twice the average peak force on the patella or kneecap in the front of the knee joint, the study found. Running also produced almost 30 percent greater average peak force on the tibiofemoral joint, or the knee hinge formed between three bones: the femur, tibia, and patella.

Skipping, however, used 30 percent more calories than running.

"Certainly, running is an integral component of many athletic activities and we are not unaware of the aversion some people may have toward performing skipping as a standard component to their physical regime, but skipping has nonetheless emerged from this study as an alternative form of locomotion with untapped potential," said lead study author Jessica McDonnell of East Carolina University in Greenville, North Carolina.

Simply put, the gait mechanics of the two types of exercise are different, and may have different outcomes for the body, McDonnell said by email.

"When people run they are executing a cyclical gait composed of alternating periods of absorption (stance) and propulsion (flight)," McDonnell explained. "Throughout the gait there is either one foot on the ground, (the) single limb support phase, or none, the flight phase."

By contrast, "when people skip (step and hop on one leg followed by a step and a hop on the opposite leg) a support phase is added not seen in running," McDonnell continued.

"The skipping gait patterns has a single limb support phase, double support phase, and a flight phase," McDonnell said. "Due to the composition and execution of the gait, skipping has reduced vertical ground reaction force, decreased step length, increased cadence contributing to the attenuation of knee compressive forces."

Beyond the different gait pattern, the greater height people typically achieve with their legs when skipping may account for additional calories burned with this activity as compared with running, McDonnell said.

The study participants ranged in age from 18 to 30; half were female. They were a healthy weight, on average, and they all participated in a training program to practice skipping for distances up to one mile on a laboratory treadmill before their gait assessments.

Then, researchers assessed participants' gait mechanics and calories expended while they ran and skipped on a treadmill at identical speeds.

It's possible that the results for people who got trained in skipping on a treadmill might not reflect what would happen in the real world if people tried both activities on their own, the study authors note.

"With both running and skipping, people generally use a longer distance between steps and quicker pace than when walking, which may lead to more force through the knee from the ground," said Mackenzie Herzog of the Injury Prevention Research Center at the University of North Carolina at Chapel Hill.

"As with any physical activity, people who run and skip should listen to their body and talk to their doctor before starting new vigorous activities or if they have questions about exercising." Herzog, who wasn't involved in the study, said by email. "Gradually increasing duration and distance, taking rest days and cross-training, and using proper equipment, especially shoes, are recommended."

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