The straps aren't tightened to the point of binding the feet in the pedals and I'm not talking about Powerstraps. This is not the same as toe clips and a cleated shoe, where the foot is locked in when the strap is tightened. The strap and clip is there to position the ball of the foot over the pedal axle - position the foot, not lock it down. Running
loose straps and clips is a nice compromise between clipless and platforms - you essentially have the freedom of plats with the foot positioning of clipless. Yes, one can't pull up much on the upstroke of the leg as when using a clipless pedal, but you can float the leg weightless on the upstroke and the foot will not drift off the pedal.
Re: Mountain biking in the 60s
Wow! My mountain biking experience in the 60s was riding a Stingray [I'd kill to still have that bike] down the gravel alley. Unless you lived in Marin County and/or include cyclocross, mountain biking didn't come onto the scene until the early '80s. BTW, my first true mountain bike was an '85 [?] Jamis Dakota, complete with axles as soft as butter, faux fillet frame brazing and a 6-speed freewheel... and of course toe clips and straps.
-Old Timer Barrry
...straps hurt the top of my feet and make me feel 'bound', ...(I met an old timer recently, he talked about platform with straps back in the sixties and mountain biking, also, 'in the sixties', really neat guy...he suggested straps, I told him I didn't like the feel, he seemed disappointed as he claimed "there was nothing like it"...