MORE THAN A CENTURY AGO, the great ocean liners, including the original Queen Mary and the ill-fated Titanic, provided space for passengers to exercise. These fitness centers of yesteryear, usually situated in rooms without so much as a porthole for views, were equipped with the iron weights and intricate wooden exercise machines of the time. Passengers worked out on rowing machines and static bicycles in full Edwardian dress, from suits and ties to dresses and hats.

For most of the 20th century, cruise ship fitness centers remained little more than windowless galleries of exercise and weight-lifting equipment. In the 21st century, however, as an increasing number of cruise passengers strive to stay shipshape, cruise lines transform fitness centers to keep up with swank land-based health clubs and workout emporiums.

Today’s biggest cruise ships offer unprecedented space and options for passengers who work out while sailing. Norwegian Cruise Line’s new 2,934-passenger Norwegian Escape elevated the fitness center to the top deck where passengers can tackle the largest rope course at sea with more than three stories of activities; ride “sky rails” which function like small zip lines; and walk “the plank,” a narrow beam jutting over one side of the ship. Norwegian’s larger vessels also sport rock-climbing walls and 24-hour gyms festooned with all the latest bells, whistles and punching bags.

Not to be outflanked, Royal Caribbean International installed SeaPlex, a high-tech indoor sports complex, on its 4,180-passenger, state-of-the-art mega-ships, Anthem of the Seas, Ovation of the Seas and Quantum of the Seas. SeaPlex is replete with a basketball court, roller skating rink, bumper car arena and circus school.

Smaller, mid-sized, all-inclusive luxury lines followed suit. Crystal Cruises now features wraparound promenades for a “walk on water” workout that employs cotton vests with pockets for weights. Viking Ocean Cruises provides dedicated running tracks that are shaded, wide and long, with as few as four laps to the mile. Oceania Cruises conducts more than two dozen fitness classes led by professional instructors, ranging from Pilates and yoga at sunrise to walk-a-mile hikes and Kinesis wall exercises. Windstar Cruises placed a fitness center enclosed in glass on its top decks, with more than 20 workout stations and a fluid rower that operates with built-in water resistance.

Even very small ships are expanding workout options by running special fitness cruises. Amadeus River Cruises’ 168-passenger MS Amadeus Silver III sails the Rhine Nov. 7–12 this year with gym visits in port and special classes hosted on board by two celebrity instructors. And UnCruise Adventures’ 84-passenger Safari Endeavor explores the Sea of Cortes March 21–28, 2020, with its own special team of fitness experts overseeing strength training and yoga, both on deck and on the beach.