A weekly session of negative only exercise has good effect....

here is one for the HIT boys: "only 30 min of eccentric exercise per week for eight weeks was sufficient to improve health risk factors".

A Weekly Bout of Eccentric Exercise Is Sufficient To Induce Health-Promoting Effects

Abstract
PURPOSE:: The effects of chronic eccentric-only versus concentric-only exercise on muscle physiology and blood biochemistry were investigated. METHODS:: Twenty women performed on an isokinetic dynamometer a concentric (n = 10, age 21.0+/-0.4 years, body fat 22.0+/-0.9%) or an eccentric (n = 10, age 20.0+/-0.3 years, body fat 23.2+/-0.7%) exercise session using the knee extensors of both lower limbs once a week for eight subsequent weeks. Muscle function (isometric, concentric and eccentric peak torque, range of movement and soreness) was evaluated before, immediately after and 48h postexercise in each one of the eight training weeks. Body fat, resting energy expenditure (REE), lipid and carbohydrate oxidation rate as well as blood chemistry measurements (lipid, lipoprotein and apolipoprotein profile, glucose, insulin, glycosylated hemoglobin and creatine kinase) were examined before and 48h post-exercise at the first and eighth week of training. RESULTS:: Acute eccentric exercise increased REE and fat oxidation at week 1 (12.7% and 12.9%, respectively) and at week 8 (0.7% and 2.8%, respectively). Chronic eccentric exercise increased resting REE and fat oxidation at week 8 compared to at week 1 (5.0% and 9.9%, respectively). Acute eccentric exercise improved blood lipid profile at week 1 and week 8. Chronic eccentric exercise improved resting blood lipid profile at week 8. Acute eccentric exercise increased insulin resistance at week 1 but not at week 8. Chronic eccentric exercise decreased resting insulin resistance at week 8. CONCLUSION:: It is reported for the first time that only 30 min of eccentric exercise per week for eight weeks was sufficient to improve health risk factors.