BodyPump and Personal Training - Changes in Muscle Strength and Body Composition

Background Regular physical activity confers protection against a number of both physical and mental health disorders (Hallal et al 2006; Bauman 2004). Physical activity also produces health benefits related to overall physical fitness and physical performance (Kruk 2007; Pedersen & Saltin 2006; Kesaniemi et al 2001). Physical activity can prevent cardiovascular diseases (Adedeji et al 2011, Anderssen & Hjermann 2000), type 2 diabetes (Admiraal et al 2011), some types of cancer (Courneya & Friedenreich 2011, Friedenreich 2001) and mental illness e.g anxiety and depression (Harris et al 2006; Pedersen & Saltin 2006). Despite knowledge of benefits of regular physical activity, inactivity is a growing global problem (Kohl et al 2012).

At the same time prevalence of overweight (BMI≤25) and obesity (BMI≤30) has doubled between 1980 and 2008. In some regions, such as Europe and America, more than 50 % of women are overweight (Perèz Rodrigo 2013). About 35 % of the world's population over 20 years suffer from overweight, and 12 % are obese (WHO, 2008). In Norway around one in five adults has developed obesity (Ulset et al 2007).

During the last two decades the fitness industry worldwide has increased considerably in both number of centers and number of members, and with this, there have been major changes in training opportunities (Bakken Ulseth 2003; Ommundsen & Aadland 2009). In 1987, 8 % of the adult Norwegian population reported to exercise at a fitness centre, compared with 25 % in 2007 (Ommundsen and Aadland 2009). Today the fitness industry is the arena most women seek when they start physical activity (Vaage, 2004), but there is very little research about factors related to physical activity among those who choose to be physically active at fitness-centres.

Resistance training has become a popular form of exercise for both women and men of all ages, and especially women do more resistance training today than in the past (Breivik, 2010). The health benefits of resistance training are many. With proper dosage and regular exercise it can increase muscle and connective tissue cross-sectional area and bone mineral density, improve functional capacity, reduce body fat, increase basal metabolic rate, decrease blood pressure, improve blood lipid values, glucose tolerance and insulin sensitivity (Kelley & Kelley 2000; Pollock et al 2000; Feigenbaum & Pollock 1999). These benefits, as well as performance-related benefits, can improve quality of life in different populations, such as those with overweight and obesity (Pollock et al 2000).

The effect on muscle strength varies between studies, which may be attributed to factors such as study design, methods and genetics. Yet untrained people can generally expect an increase in 1RM (one repetition maximum) of 30-40 % after 12 weeks (Raastad et al 2010). Increase of muscle volume (hypertrophy) in untrained individuals seems to be best achieved at a load of 60-80 % of 1 RM (6-15 repetitions). Increase in maximum strength for untrained is located at 70-85 % of 1 RM (4-8 reps), while local endurance strength is at 20-60 % of 1 RM (15 repetitions or more) (Raastad et al 2010).