I recall reading from numerous "old school brethren" that as Iabadman stated, ran or they would use diet and low carbs, plus a rather frantic pace while working out.
In contrast, some people like the killer..Danny Padilla would ride a stationary bike for 2 hours a day while prepping for contest.
Now you know back in the day they pretty much all trained the same way...Here is a quote for Danny on his cardio views with his training partner the legend Ed Corney:
JB: Ed has said that you guys were doing a six-day double split workout at that time.
DP: Right, we were doing basically the same stuff that Arnold and he had done. All of us were doing a double split. We would do Chest and Back on one day, Legs at night and Shoulders and Arms on another day, etc., then I was the first . . . well, I don’t know if I “taught” him this, or he did it on his own . . . but I basically, at that point, tried to emphasize a little aerobics. He had never done cardio and I was telling him “Well, as we age It’s very good to do cardio.” It was always important in my training because of the fact that in my family there was a history of heart problems . . . so, I kind of emphasized that to him and he ended up liking it.
So you’re 5’2”, and you were planning on hitting the show at what weight?
DP: Well, at the time, I was hoping to hit it at about 175-180 lbs. I had been training all year and my bodyweight had reached the high 180’s, low 190’s. By the time I tightened down on the diet, cut down on the calories and carbs, I had bottomed out in the mid-170’s.
JM: You seem to have an unusual style of contest prep.
DP: I still believe in the old high protein, low carb diet. I consume as much protein as I can, six to eight pounds of meat a day. I also incorporate a certain amount of aerobics, but it’s usually an aerobic workout where I’m not straining the whole body, you can’t go out there and run seven miles or even jog. I’ll use the stairmaster or a lifecycle. The closer it comes to the show; of course, I’ll cut the carbs down. I was probably on 150 to 200 grams of carbs per day for most of the year. Then about two months before the show I went down to about 100 grams of carbs per day. Three months before the show I decided to use the old Arnold training regimen that we had used when I was out there in California. We worked each bodypart three times a week. Of course they told me, that because I was an old man, it wouldn’t be possible for me to grow on an intense schedule like that. Well, I passed up all the young guns in my gym.
JM: So, let me get this straight. You’re training each body part three times a week on a double-split and you’re still growing?
DP: I was still growing, absolutely. I would just increase the calories. It’s all about calories, you must feed the machine. I would train chest and back in the morning, legs at night. Then I would train shoulders and arms the next morning plus calves and abs then next night. I would start the routine all over again Wednesday. And I grew on it.
JM: Along with how much cardio?
DP: At that time, I was doing 20 minutes exactly. Then about two weeks before the show, I started doing 30 to 40 minutes on the stairmaster and as much as an hour on the lifecycle.
The old school still rules, I don't care what anyone says...High protein/fat and low carbs = Shredded inside out!! They loved their beef. fish chicken, eggs. etc.