High Intensity Interval Training (HIIT) has been shown to be as effective as longer duration steady state cardio for promoting fitness. A new study published in the journal Medicina dello Sport looks at what can be accomplished with a relatively short 2-week period of HIIT where recreationally active women trained 5 times each week to exhaustion.
Subjects had a variety of values measured before and after the training program. They also took Wingate anaerobic tests twice during each workout. Peak power, time to exhaustion and peak carbohydrate oxidation increased, while rates of maximal fat oxidation remained the same.
General Fitness

As a general rule, you should allow at least 48 hours for each muscle group to recover from weight training. Exercising different muscles on different days is one way to work around this schedule, but a study published in the Journal of Strength and Conditioning Research suggests super sets might require a different approach.
Twenty-five physically active men performed 5 sets of 8 to 10 reps max on 4 different exercises: 2 targeting the legs and 2 for the shoulders. Some did super sets while other subjects separated these exercises. Super sets generated higher muscle activity as well as markers of muscle damage. Researchers concluded that 5 days was not enough time for complete muscle recovery.

Lots of people sign up for gym memberships with the intention of getting into shape. Inevitably, many quit because the effort seems too difficult. Research from the Department of Sport Science at the University of Freiburg suggests your expectations can influence how hard exercise seems. Findings were published in the journal PLOS ONE.
Seventy eight men and women aged 18 to 32 watched videos promoting the positive effects of exercise and the cycling enhancing properties of a compression shirt they put on before riding a stationary bike for 30 minutes. Others watched skeptical videos about exercise which included negative opinions about the garment. Every 5 minutes during exercise they were asked to rate the strenuousness of the effort.
Results showed that training felt less strenuous when subjects started out with a positive attitude. This effect was strongest in subjects who thought they were athletic. Positive reinforcement didn’t seem to help people who self-described as less active.