Build lean muscle. The Slow Rep = the Grow Rep

not an example of light weight

When researchers were trying to tackle the issue of building muscle for an older population (age 50-70), they had a few problems: This population can be prone to high blood pressure, sometimes risk of stroke, they face natural muscle wasting (Sarcopenia), and sore joints that can't handle heavy weights.  Since lifting heavy is known to increase blood pressure during the workout, this demographic really has the deck staked against them.

What they learned can help us all, especially those who don't have access to a lot of equipment.

How do you build muscle without lifting heavy weights? 

It is well recommended that to gain significant muscle tissue, one needs to lift in the 80%+ range of their one-rep maximum (1RM).  Example: if you can bench press 200 pounds, 1 time and one time only, then your 1RM is 200#.  If you want to gain peak strength you need to perform sets with 160# or more in order to really stimulate those muscles for growth.  Of course peak strength is not the only thing to develop there is also endurance and power, but we'll stick with strength for now.

Japanese researchers discovered muscle mass could be built using 50% of the one rep max if the proper technique was observed.  This allowed them to build muscle without spiking blood pressure.  The key to this technique is not only moving slowly, but also to make sure your muscles don't get to "take a breath".  I'll explain.

Many people like to rest in the "locked position".  With a squat, this is standing fully upright; with the pushup, this is arms locked out or paused with your chest on the ground.  In either case, your muscles are getting a break and that break is allowing more blood to flow in.  This gives the muscle more oxygen and makes you feel better.

With the Slow Rep (or Temp Rep, as I've seen it called by others), you take 3 seconds to go from the top position to the bottom position, you pause at the bottom for one second (with the pushup - this is NOT resting your chest on the ground), then take 3 seconds to return to the top position.  Don't rest at the top at all! Continue to the next rep: 3 seconds down, 1 second pause at the bottom and 3 seconds up.

It is the starving of your muscle for oxygen that results in physical growth and strength increase (technically, the lack of oxygen stimulates intra-muscular enzymes that promote growth).

Finally, the researchers took nearly every set to failure.

Some ideas:

Try mixing up your interval training.  Instead of doing all your reps as fast as you can, try them all using the Slow-Rep or Tempo-Rep tecnique.

Another thing you can try is 5 Slow-reps immediately followed by 10 normal ones.  This brings a great burn!

BTW, that is a real picture.