Introduction

Increases in muscle growth is a complex process driven at the cellular level by protein accumulation into contractile and non-contractile proteins. Muscle growth in adults is believed to occur via increases in cell size (hypertrophy) rather than increases in cell number (hyperplasia) [9][24][33]. Muscle growth is desired by various populations ranging from cancer patients [1] to NFL football players [13], and in particular, bodybuilders [11]. There are numerous factors that may influence and or have been associated with skeletal muscle hypertrophy including hormones [30][31], nutrition (namely protein intake), and resistance training [21][22]. A variable that has been studied and debated by researchers, clinicians, and bodybuilders is the use of partial range of motion (pROM) compared to full range of motion (fROM) for strength, hypertrophy, and power. Strength outcomes have been the major factor investigated in these experiments and more often than not fROM is most often generalized as most beneficial which has been generally attributed to a greater amount of mechanical stress about the whole length of the muscle [5][8][11][17][18]. However, some of these same studies along with others show some benefit to pROM in either strength outcomes, hypertrophy, and rehabilitative protocols [10]. The purpose of this article is to focus on the effects of pROM during RT on hypertrophic outcomes and to elaborate some of the research and factors that may influence a hypertrophic response in conjunction with the use of pROM in RT bouts.

 

Resistance Training: Intensity, Volume, and Range of Motion

The American College of Sports Medicine published a position stand in 2009 suggesting an intensity or load of ~70–85 % of 1 repetition max (1RM) for 8–12 repetitions per set for one to three sets per exercise and most time training spent in the 6-12 repetition range for optimal muscular hypertrophic responses [2]. However, this stand disregards range of motion (ROM) as a functional factor that may or may not influence hypertrophic responses. This may be due to fewer studies comparing pROM to fROM by observing functional strength outcomes. Full ROM is defined as the amount of movement about a joint, which is dependent upon the joint articulation, classification, and the plane or axis the movement takes place. Similarly, in relation to skeletal muscle, full range of muscle work is defined as a muscle from a position of full stretch to a position of maximal concentric contraction [6]. Recently, there have a handful of research training studies assessing muscle growth and strength outcomes in response to pROM vs a traditional fROM. Pinto, et al compared two RT groups, untrained, utilizing seated machine bicep curls, for a 10-week training period. The fROM group performed elbow flexion with (0° to 130° of elbow flexion, where 0° is full elbow extension), while the pROM group performed elbow flexion (50°to 100°). Both groups showed the same muscle gain or muscle thickness (MT) increase over the training period. The fROM group showed an increase of 9.7 %, comparatively to pROM which had 7.8 % increase, though were not significantly different, meaning NOT DIFFERENT or same. However, in relation to strength outcomes, fROM showed a greater 1RM increase then did pROM above baseline values, which would support fROM as better form of ROM for strength desired outcomes. However, in regards to muscle hypertrophy, based on the data, both fROM and pROM seem to be similar. The authors make a unique suggestion in regards to pROM and multijoint resistance exercise movements stating that ‘different muscles contract at differing lengths throughout the full ROM, each of the muscle groups may not be at optimal lengths for force production. Hence, for any given joint angle, some musculature may produce their maximal force whereas others are at less than optimal length to do so’ [23].

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