Muscle activations under varying lifting speeds and intensities during bench press

Abstract

During a set of resistance exercise performed until exhaustion, the relationship between intensity and the number of repetitions can be affected by lifting speed, with faster speeds producing higher numbers. The hypothesized mechanisms include enhanced utilization of the stretch-shortening cycle. This study investigated muscle activations under varying speeds and intensities during bench press using surface electromyography (EMG) to suggest further mechanisms for the above finding. Thirteen weight-trained men (21.7 ± 3.6-year-old) performed bench press until fatigue under five intensities (40-80% 1RM), and four speeds (slow 5.6-s/repetition, medium 2.8-s/repetition, fast 1.9-s/repetition, and ballistic maximum speed). Surface EMG was recorded from the pectoralis, deltoid, and triceps for root-mean-square amplitude and median frequency. EMG amplitudes were greater for faster and heavier conditions before fatigue. Faster conditions, however, produced a significant fall in amplitude during the final concentric phase compared to slower movements. After fatigue, EMG amplitude increased, with the speed effect being maintained. The intensity effect on amplitude either disappeared or remained similar, depending on the muscles. Median frequencies before fatigue were similar among speeds and intensities. The fall in frequency after fatigue was similar across speeds, but greater for lighter intensities. It was concluded that reduced muscle activation during the final concentric phase in faster conditions allowed a better muscle pump, explaining the increased repetition numbers. Fatigue levels are likely to have been similar across speeds, but greater for lower intensities. An incomplete rise in EMG amplitude after fatigue for lower intensities could imply an increased contribution of central fatigue or neuromuscular transmission failure.

Physiological stimuli necessary for muscle hypertrophy

“…These mechanisms may increase the rate of muscle protein synthesis through activation of anabolic and/or prevention of catabolic signaling pathways, leading to hypertrophy [23][24][25][26] as well as the proliferation of satellite cells 27) . The fact that low load exercise imposes greater metabolic stress has been demonstrated by a previous EMG study 28) . The median power frequency of working muscles (bench press at 40, 50, 60, 70 or 80% 1RM) after repetition failure was greater for lower exercise loads, which incurred greater numbers of repetitions and longer exercise durations, than higher loads.…”

Attempting to better define “intensity” for muscular performance: is it all wasted effort?

“…We suggest that this usage is inaccurate, both here and more widely, with reference to the percentage of one repetition maximum (%1RM), e.g. the higher the %1RM, the higher the intensity (Sakamoto and Sinclair 2012). However, %1RM is simply a reference to load.…”

“…We read with interest the recent publication ''Muscle activations under varying lifting speeds and intensities during bench press'' (Sakamoto and Sinclair 2012). In the title and throughout this paper, the term intensity is used.…”

“…Sakamoto and Sinclair 2012). Speed, by definition is a product of the time taken to move a given distance.…”

“…Interestingly, Sakamoto and Sinclair (2012) state that they did measure vertical bar displacement using a string potentiometer, with an absolute error of less than or equal to 1 mm. However, it is unclear as to whether this was used to control or maintain the distance the bar was moved for each repetition, between participants, or simply to measure the speed.…”