The Interborough Rapid Transit subway line opened in New York City in 1904, running for around 10 miles between City Hall and 145th Street in Manhattan. But it got longer and stronger over the decades, becoming a major part of the city's 248-mile subway system.

Another form of IRT — isometric resistance training — can help you run longer and stronger too. It does that by placing tension on muscles without any motion in your surrounding joints or any lengthening and contracting of the muscles.

According to a new study published in the journal Nature, IRT is a safe and effective way to lower your blood pressure.

Looking at data from 24 trials, researchers found that regularly doing IRT using a simple handgrip lowered systolic blood pressure by almost 7 mmHg and diastolic blood pressure by almost 4 mmHg.

And you can easily sneak IRT into your day. It takes only 12 minutes two to three days a week to see positive results using a handgrip device (or just making a fist very intently).

Other forms of IRT include planks, ab/core contractions, and the wall sit — a workout for quadriceps, hamstrings, and glutes. Here’s how you do it:

1. Stand about two feet from a wall and lean your back against it.

2. Sink down so your thighs are parallel with the floor, if possible.

3. Hold for 15 seconds.

4. Aim for five rounds of 15 seconds each.

For other IRT exercises, Google "isometric exercises" and watch the videos you find. But start slowly. You want to contract your muscles, not contract an injury.