What About Speed?
"I might look good, but will I be faster?"
Recent studies on trained and untrained (sedentary) cyclists have shown positive results. In one study, untrained cyclists who strength trained for 12 weeks improved their cycling endurance by 33 percent and lactate thresholds by an average of 12 percent. The control group, which did no strength training, made no gains.
In a separate study, the addition of a strength-training program increased cycling endurance by 20 percent, allowing cyclists to pedal 14 minutes longer before fatigue set in. They also increased short-term, high-intensity endurance (performance in the 4- to 8-minute range) by 11 percent.
Studies on Triathletes
Admittedly, studies on cyclists' and triathletes' training plans over long periods of time are limited. This makes it difficult to determine if strength training is essential for triathletes seeking to improve performance or not.
I did find one study that examined the training of world-class female triathlete Ainhoa Murua over the course of 50 weeks as she prepared for the 2012 Olympic Games. In her 50 weeks of preparation, she completed 796 training sessions consisting of 303 swims, 194 bike rides, 254 runs and 45 strength-training workouts. Over the course of her year, she improved her world rank from 14th to 8th and placed 7th at the Olympic Games.
Did strength training contribute to her success? Her results were unarguably great. Would she have done as well without a strength program? We just don't know.
In summary, how important a weight-training program might be to triathletes is not quantitatively known at this time.