Activating the clavicular bundle
Over the past 20 years or so, incorrect information has been circulating about techniques designed to activate the clavicular bundle, one of the three sections of the greater pectoral muscle (pectoralis major). Whether we are targeting certain areas of weakness or simply trying to sculpt our bodies more precisely, we owe it to ourselves to obtain accurate information if we wish to obtain the desired results. For example, merely increasing the incline of the bench press will place a greater strain on the clavicular bundle. However, scientists have been in disagreement on this point since 1995! Let's review the findings of a few relevant studies and take a look at some specific details that will make a real difference to your training routine and help you maximize your gains.
Grip width Overhand grip width has no influence on clavicular bundle activation (Barnett, 1995). However, using a reverse grip (underhand) at 200% of the biacromial width (i.e., width across the shoulders) increases the degree of muscle activation by 27% compared with the other grips analyzed (narrow, middle and wide). The figures in the table below are percentages of the stress placed on the clavicular bundle compared with the benchmark (wide grip), which corresponds to 200% of the biacromial width. Middle grip corresponds to 100% of the biacromial width, while narrow grip corresponds to a fist's-width distance between both hands. foward-grip-reverse-grip Although underhand grip is not usually seen in gyms nowadays, it has been used for decades in strength contests. In a contest featuring the underhand grip bench press, one of the best performances was recorded by Rick Weil, who lifted 551 lbs. even though his body weight was only 181 lbs.! This lift was equivalent to 3.06 times his body weight (see table below). raw-bench-press-records
Bench angle Another study (Barnett and coll., 1995) analyzed four bench press positions: an 18-degree decline (-18°), flat, a 40-degree incline (+40°) and vertical. The results show that the incline bench (+40°) made greater use of the clavicular bundle than the decline bench did (-18°). However, when compared with the flat bench press, this difference was insignificant (see adjacent illustration). Therefore, according to this study, both the decline bench press and the incline bench press activate the clavicular bundle. trunk-inclinaison A concurring study notes that the incline and decline bench presses place similar levels of stress on the clavicular bundle (see figure below) (Glass and Armstrong, 1997). This had been previously demonstrated by Barnett and coll. (1995) in their own testing, although the degree of activation was significantly different. This was due in part to the fact that in the first study (Barnett and coll., 1995), the incline angle was 40°, whereas in the second study (Glass and Armstrong, 1997), it was 30°. In addition, the electrodes used for the measurements were placed in different positions and were placed slightly lower in the group tested by Barnett and coll. (1995), which may well explain this positive difference. The decline angle was different as well: in the second study, it was -15° (i.e., a total difference of 45° between the two positions), whereas in the first study, it was -18° (i.e., a difference of 58° between the two positions). bench A third study (Trebs and coll., 2010) analyzed four angles on a Smith machine bench press (0°, 28°, 44° and 56°). This study found a significant difference in clavicular bundle activation between 0° and 44° and 56°, i.e. larger angles than those studied by Barnett and coll. (1995) and Glass (1997), which were 40° and 30° respectively. This difference may also be due to the fact that the testing was performed on a Smith machine, which limits the bar's vertical range of motion and prevents the normal "S" or reverse "C" shapes usually seen on a free-bar bench press. It is safe to assume that this may have had a positive effect on clavicular bundle activation. More recently, a fourth study (Lauver and coll., 2016) analyzed four bench press angles (0°, 30°, 45° and -15 °). In terms of clavicular bundle activation, the authors concluded that there was no significant difference, whatever the angle. This is in line with results reported by Barnet and coll. (1995) and Glass and Armstrong (1997).

Clavicular bundle activation according to shoulder angle pectoralis-major The above image (Inman and coll., 1944) shows the degree of activation of three bundles of the greater pectoral (clavicular, sternocostal and abdominal) with shoulder flexion/abduction movements. It is worth noting that clavicular bundle activation reaches an initial peak at 75° shoulder flexion and reaches maximum stimulation at a flexion angle of 120°.
Summary Based on current scientific data, the optimal position for maximizing activation of the clavicular bundle (greater pectoral) is a reverse grip with a width corresponding to twice your biacromial width (200%). In addition, if the data for clavicular bundle stimulation with shoulder flexion (Inman and coll., 1944) are combined with those of other studies (Barnett and coll., 1995; Lauver and coll., 2016, Armstrong and Glass, 1996; Glass and Armstrong, 1997), an underhand grip with a 200% biacromial width and a 30° incline (in order to obtain a 120° shoulder abduction angle) will provide maximum muscle activation. Furthermore, according to Trebs and coll. (2010), only using an overhand grip on an incline Smith machine bench press would activate the clavicular bundle to any greater degree (this is not possible on a free-bar bench press).  


Have a great workout!

Sources •    Armstrong T, Glass SC (1996) Motor Unit Recruitment of the Pectoral Muscle During Incline and Decline Bench Press Exercise. Medicine & Science in Sports & Exercise. May - Volume 28 - Issue 5 - p 206. •    Barnett, C., Kippers, V., & Turner, P. (1995) Effects of variations of the bench press exercise on the EMG activity of five shoulder muscles. Journal of Strength & Conditioning Research. 9(4):222-227. •    Glass, S. C., Armstrong, T. (1997) Electromyographical activity of the pectoralis muscle during incline and decline bench press. Journal of Strength & Conditioning Research. 11(3):163-167. •    Inman T, Saunders M et Abbott C. (1944) Observations on the function of the shoulder joint. J Bone Joint Surg Am. 26:1-30. •    Lauver JD, Cayot TE, Scheuermann BW. Influence of bench angle on upper extremity muscular activation during bench press exercise. Eur J Sport Sci. 2016;16(3):309-16. doi: 10.1080/17461391.2015.1022605. Epub 2015 Mar 23. •    Trebs, A. A., Brandenburg, J. P., & Pitney, W. A. (2010). An electromyography analysis of 3 muscles surrounding the shoul- der joint during the performance of a chest press exercise at several angles. Journal of Strength and Conditioning Research, 24, 1925–1930.

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