Eccentric and Concentric Bench Press Comparison

Introduction

Resistance training is an exercise modality that can be defined as a movement working against an external load resulting in physical adaptations (McArdle, Katch & Katch, 2014). It is utilised by many as a means of increasing muscular strength, improving athletic performance, reducing the risk of injury and to maintain a healthy lifestyle. An average resistance training programme would incorporate a variety of static and dynamic movements whilst under an external load (Jones, 2009). Whilst the muscles are static, the fibres are in a fixed state and no change in length occurs. However, in a dynamic movement muscles go through a shortening and lengthening process. The concentric phase involving the shortening of muscle fibres, and the eccentric phase involving the lengthening of the fibres. Current literature proposes that eccentric and concentric training illicit different training responses and therefore could produce different muscular adaptations (Rosete et al. 2015).

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Although there are a variety of methods to provide resistance in a training sense, traditional exercises involve moving a load in opposite directions (i.e. push/pull) where there is a shortening (Concentric) and subsequent lengthening of the muscles (Eccentric). Proske (2001) describes the concentric phase as the actions that initiate movement, whereas the eccentric phase slows movement or brings it to a halt. Some research indicates that muscles acting in an eccentric fashion produce more force than when working concentrically. Other research shows eccentric movements have different fatigue patterns to concentric movements which could explain their apparent superiority. The intended purpose of this proposal is to quantify if concentric bench press yields less strength than eccentric bench press, measured via a 1 rep max max test.

Literature Review

As previously defined, resistance training is movement working against an external load resulting in physical adaptations. The health benefits of resistance training are widely documented with most of the literature reporting on musculoskeletal adaptations. Recently there has been an emergence of literature detailing other outcomes of resistance exercise such as benefits for metabolic disease (Jurca, 2005), bone density & health (Lohman et al, 2003), all-cause mortality (Metter et al, 2002), mobility (Janssen et al, 2002) and quality of life (Levinger et al, 2007). Furthermore, resistance training provides a means of exercise for people whose current cardio vascular based regimes such as jogging or swimming have become too difficult. Based on these findings, resistance exercise is now considered an imperative component of a regular training program.

The eccentric phase of a muscle action is when the force generate by a muscle is inferior to the external load. This is characterised by a lengthening of the muscle even though an actin-myosin cross bridge is formed. In this instance when actin separates from myosin it is regarded as a mechanical separating rather than chemical (Flint & Hurst, 1978). In contrast, a concentric muscle action involves the actin filaments being pulled over the myosin filaments as the muscle shortens. This is commonly known as the Sliding Filament Theory (SFT).  SFT refers to the movement of actin and myosin sliding over one and other. (Baechle & Earle, 2000). Cross bridges are separated through the splitting of an Adenosine Tri Phosphate molecule, thus making it a chemical reaction rather than mechanical. This is a more energy dependant process and should result in less trauma to the muscles.

Eccentric muscle action, when used in a resistance training setting has been shown to improve neural activation (Enoka, 1996), muscular strength (Hortobagyi, 1996) and increase muscle size (Vikne et al, 2006). Enoka (1996) goes on to suggest that muscles become more resistant to fatigue when working eccentrically. Placing emphasis on the eccentric phase of an exercise has been proven in some studies to be effective at improving strength than an even split of eccentric/concentric (Brandenburg & Docherty, 2002).

Research has been conducted to examine the physiological and metabolic effects of concentric actions versus eccentric muscle actions. A study by Hollander et al, (2008) examined if contraction type (Eccentric/Concentric) or load (Absolute/Relative) has a greater metabolic impact on resistance exercise. Seven resistance trained men were included in the study. Their concentric 1 rep max determined for several exercises then their 1 rep max for eccentric was estimated at 20% greater. On completion of the initial 1 rep max testing, participants completed a further 2 bouts of maximum lifts in a random order: concentric only lift and an eccentric only lift. They were then assessed on rating of perceived exertion, pain rating and heart rate. Tests were conducted to take samples of blood PRE/POST exercise, and 15 minutes after exercise had finished to identify lactate and cortisol levels. To analyse the data, a repeated-measure ANOVA was used. No differences were noted between concentric and eccentric trials for pain rating and perceived exertion. Heart rate was significantly higher in every exercise except lat pulldown. Levels of lactate were significantly higher directly post exercise and 15 minutes after following concentric training compared to eccentric training. The study shows that at a relatively lower intensity, concentric and eccentric training show similar rate of perceived exertion & pain perception under a relative load (%eccentric1RM= %concentric1RM +20%).  This suggests that you can overload the eccentric phase of an exercise with 20% more than the concentric phase and the body is not negatively affected. Heart rate was maintained at a lower threshold throughout training apart from in one instance despite the eccentric phase holding a 20% greater load. This potentially indicates that eccentric exercise could be deemed as a safer modality of exercise than concentric

Enoka (1996) conducted a study highlighting the differences in concentric and eccentric muscle actions in regards to neural activity. Previous studies suggest that neuralogical factors can augment strength gains in trained (Edgerton et al, 1986) and untrained individuals (Komi, 1986) whilst also increase the efficiency in which they can lift sub-maximal loads (Ploutz et al, 1994). It is also noted that neural factors increase the synchronization of motor units (Milner-Brown et al, 1975). A motor unit is defined as motoneuron and all its associated fibres (Bachle & Earle 2002). An action potential is passed through the motor neuron, this releases a hormone which passes across a neural junction resulting muscle fibre activation (Baechle & Earle, 2000). To increase the force generated by a muscle, motor unit activation must increase frequency, or recruit more motor units at once. Usually motor units activate in a uniform sequence, inferior units  activate first with superior units coming in to play when the external load becomes too great, commonly termed as the size principal (Baechle & Earle, 2000). In order to generate maximum force, it is necessary for all of the motor units within a muscle to activate. In most people the size principle applies, lower threshold units being activated then the higher threshold as the load increases. Some research suggests that resistance exercise increases the efficiency that a person can recruit the higher threshold motor units (Sale, 1987). Enoka (1996) goes on to suggest that this differs for muscles working eccentrically. Research has identified that it is not likely to recruit all motor units during maximum eccentric contraction despite that fact that eccentric strength is usually 20% greater than concentric (Tesch et al, 1990).

Aims

Previous literature suggests that the strength of the eccentric portion of an exercise can be anything up to 120% greater than that of concentric (Hortobagyi, 1990). Current literature also proposes that eccentric and concentric training illicit different training responses and therefore could produce different muscular adaptations (Baechle & Earle, 2000). From the previously mentioned literature, the following was hypothesised:

– Eccentric 1 Rep Max bench press will yield greater strength than concentric.

Objectives

The main objective of this proposal is to quantify the differences in eccentric and concentric bench press scores.

Methodology

Participants

Twenty six males between the ages of 18 and 31 who have been taking part in resistance training for over 1 year volunteered for the study. For the purposes of this study resistance training experience is defined as having regularly trained bench press( 1p/w) over the year leading up to the study. Volunteers for the study where students recruited from sport and exercise science classes at The University of the West of Scotland, Hamilton Campus. It was required of the students involved in the study to firstly complete a Physical Activity Readiness Questionnaire to ensure that they were physically fit enough to engage in the study. It was also required of the students to complete an Informed Consent document outlining how the study would be carried out, how it affects them and highlighting that they have the right to withdraw themselves at any time. Exclusion criteria from the study included: orthopaedic injuries, hypertension, cardiovascular issues and abuse of anabolic agents.

Current dietary intake will not be monitored throughout the study, but it will have to remain consistent throughout its entirety. Once the study begins, participants may not take part in any resistance training out with study. The assumption is made that all participants will follow all testing protocols relayed to them for completion out with the laboratory. The participant is also required to abstain from exercise that is greater than the needs for daily living during the testing period. They must also refrain from taking any ergogenic supplements or making dietary changes throughout the testing period.

Protocol

The study will consist of 3 testing sessions over an 8-week period. Testing will be conducted in the strength and conditioning laboratory in the University of the West of Scotland, Hamilton Campus. Participants will be split into 2 even groups for testing, concentric and eccentric. Participants will be prompted to complete an informed consent document providing their approval to take part in the study. Once the document is completed and reviewed, anthropometric measurements will be taken: weight, height and body composition. Following anthropometric measurements, participants will perform a cardiovascular warm up on a cycle ergometer for (90RPM – 5 minutes). This will be followed by an incremental warm up protocol for bench pressing (10,5 and 3 repetitions). The weight used here will be self-selective and should increase with every set (Baechle & Earle, 2000). All three testing sessions will include the cardio vascular warm up, bench press warm up followed by 1 Rep Max testing in either eccentric/concentric bench press, depending on what group the individual has been placed in. Participants will be allowed to have a few practice attempts with an unloaded barbell to familiarise themselves with how the testing will operate.

The concentric group will perform their lifts by lying supine on a bench from the chest until they can fully straighten their arm, extending the elbow. The bar will be lowered down to their chest prior to each rep to ensure that only a concentric muscle action is being measured. This will be done via a pulley system and two additional spotters positioned at either end of the barbell. When the participant is unable to completely straighten the arms to complete the concentric bench press, the repetition will be deemed a failed rep.

The eccentric bench press will involve the slow and controlled lowering of a barbell from full extension down to the chest. It should take the participant three seconds to perform this movement and tempo will be kept with a metronome to help to identify successful reps. On completion of a rep the barbell will be returned to the original position via pulley system and assistance from spotters. If the participant is unable to control the descent of the bar, allowing it to touch their chest before the 3 seconds ends the repetition n will be classed as a failure.

To ensure that all the participants are safe, stringent measure will be taken. Spotters will be used during all exercise sets, warm up and testing. The pulley system will be lowered to the appropriate height for each user, this will be marked to ensure consistency with the operator. Chalk will be made available on request to reduce the likelihood of the barbell slipping from the hands.

Statistics

All data collected in the study will be analysed using an SPSS software. The data will be initially inspected to make sure it is acceptable. The mean and standard deviation will be calculated using a paired T test which will help to identify if there is a significant difference between concentric one repetition maximums and eccentric.

References

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