refers to the total number of muscles worked, exercises, sets, and reps, either during a single session or measured over a longer period. Frequency refers to how many training sessions are performed per week. A training frequency of two times per week has greater effect on muscle size than once per week. Whether training a muscle group three times per week is superior to a twice-per-week protocol remains to be determined. Training volume has more effect on muscle strength than training frequency. A common training strategy is to set the volume and frequency the same each week (e.g. training 3 times per week, with 2 sets of 12 reps each workout), and steadily increase the resistance on a weekly basis. However, to maximize progress to specific goals, individual programs may require different manipulations, such as decreasing the resistance, and increase volume or frequency. Periodization A meta-analysis found that periodized training yields better strength improvements than non-periodized training. Making program alterations on a daily basis (daily undulating periodization) has similar effect to other periodization models. Training Splits A training split refers to how the trainee divides and schedules their training volume, or in other words which muscles are trained on a given day over a period of time (usually a week). Popular training splits include full body, upper/lower, push/pull/legs, and the "bro" split. Some training programs may alternate splits weekly. Equipment Commonly used equipment for resistance training include free weights—including dumbbells, barbells, and kettlebells—weight machines, and resistance bands. Some bodyweight exercises do not require any equipment, and others may be performed with equipment such as suspension trainers or pull-up bars. Aerobic exercise versus anaerobic exercise Strength training exercise is primarily anaerobic. Even while training at a lower intensity (training loads of ~20-RM), anaerobic glycolysis is still the major source of power, although aerobic metabolism makes a small contribution. Weight training is commonly perceived as anaerobic exercise, because one of the more common goals is to increase strength by lifting heavy weights. Other goals such as rehabilitation, weight loss, body shaping, and bodybuilding often use lower weights, adding aerobic character to the exercise. Except in the extremes, a muscle will fire fibres of both the aerobic or anaerobic types on any given exercise, in varying ratio depending on the load on the intensity of the contraction. This is known as the energy system continuum. At higher loads, the muscle will recruit all