Links to said studies?
main 2 studies on decline/incline for maximum pec development:
Electromyographical activity of the pectoralis muscle during incline and decline bench presses
The purpose of this study was to determine the relationship between motor unit recruitment within two areas of the pectoralis major and two forms of bench press exercise. Fifteen young men experienced in weight lifting completed 6 repetitions of the bench press at incline and decline angles of +30 and -15[degrees] from horizontal, respectively. Electrodes were placed over the pectoralis major at the 2nd and 5th intercostal spaces, midclavicular line. Surface electromyography was recorded and integrated during the concentric (Con) and eccentric (Ecc) phases of each repetition. Reliability of IEMG across repetitions was r = 0.87. Dependent means t-tests were used to examine motor unit activation for the lower (incline vs. decline) and upper pectoral muscles. Results showed significantly greater lower pectoral Con activation during decline bench press. The same result was seen during the Ecc phase. No significant differences were seen in upper pectoral activation between incline and decline bench press. It is concluded there are variations in the activation of the lower pectoralis major with regard to the angle of bench press, while the upper pectoral portion is unchanged.
fulltext:
http://www.edulife.com.br/dados/artigos/educacao%20fisica/muscula%C3%A7%C3%A3o%20e%20condicionamento%20fisico/eletromiografia%20do%20peitoral.pdfand :
Effects of Variations of the Bench Press Exercise on the EMG Activity of Five Shoulder Muscles
This experiment investigated the effects of varying bench inclination and hand spacing on the EMG activity of five muscles acting at the shoulder joint. Six male weight trainers performed presses under four conditions of trunk inclination and two of hand spacing at 80% of their predetermined max. Preamplified surface EMG electrodes were placed over the five muscles in question. The EMG signals during the 2-sec lift indicated some significant effects of trunk inclination and hand spacing. The sternocostal head of the pectoralis major was more active during the press from a horizontal bench than from a decline bench. Also, the clavicular head of the pectoralis major was no more active during the incline bench press than during the horizontal one, but it was less active during the decline bench press. The clavicular head of the pectoralis major was more active with a narrow hand spacing. Anterior deltoid activity tended to increase as trunk inclination increased. The long head of the triceps brachii was more active during the decline and flat bench presses than the other two conditions, and was also more active with a narrow hand spacing. Latissimus dorsi exhibited low activity in all conditions.
also more studies were done by tudor o bompa for his book serious strength training - which i own:
Electromyographical (EMG) Research is an essential research tool allowing physiologists to determine the role of muscles during specific movements. EMG is a scientific method of measuring the level of excitation. This is done by placing electrodes over your body and recording the level of muscle activity induced by an exercise. A study was conducted to find which exercises cause the greatest amount of activity within each muscle group and, as a consequence, determine which exercises will produce the greatest gains in mass and strength. This study was conducted by Tudor O. Bompa, PhD & Lorenzo J. Cornacchia. Both men and women were used in the sudy and all subjects had at least two years experience with resistance training.
Here are the results of that study:
(100% would signify maximum muscle fiber stimulation)
Pectoralis Major
Decline dumbbell bench press ----------------93%
Decline bench press, Olympic bar(OB)---------89
Push-ups between benches --------------------88
Flat dumbbell bench press -------------------87
Flat bench press (OB) -----------------------85
Flat dumbbell flyes --------------------------84
Pectoralis Minor
Incline dumbbell bench press ----------------91%
Incline bench press (OB) --------------------85
Incline dumbbell flyes -----------------------83
Incline bench press (smith machine) ---------81
Medial Deltoids
Incline dumbbell (db) side laterals ----- 66%
Standing db side laterals -------63
Seated db side laterals -----62
Cable side laterals -----47
Posterior Deltoids
Standing db bent laterals ----- 85%
Seated db bent laterals -----83
Standing cable bent laterals -----77
Anterior Deltoids
Seated front db press -----79%
Standing front db raises -----73
Seated front barbell press -----61
Biceps brachii (long head)
Preacher curls (Ob) -------------------- 90%
Incline seated Db curls (alternate) ------ 88
Standing biceps curls (Ob/narrow grip)--- 86
Standing Db curls (alternate) ----------- 84
Concentration Db curls ------------------ 80
Standing curls (Ob/wide grip)------------ 63
Standing E-Z curls (wide grip) ----------- 61
Triceps brachii (outer head)
Decline extensions (Ob) ------------------ 92%
Triceps pressdowns (angled bar) ----------- 90
Dips with a bench --------------------------87
One-arm cable extensions (reverse grip) - 85
Overhead rope extensions ------------------ 85
Seated one-arm Db extensions (neutral grip)- 82
Close-grip bench press (Ob) --------------- 72
Latissimus dorsi (back)
Bent-over Bb rows ---------------------------93%
One-arm Db rows -----------------------------91
T-bar rows ----------------------------------89
Lat pulldowns to the front ------------------86
Seated pulley rows --------------------------83
Rectus femoris (quads)
Safety squats (90 degree angle, shoulder width stance) ----88%
seated leg extensions (toes straight) -------86
Hack squats (90 degree angle, shoulder width stance) ----78
Leg press (110 degree angle) ----------------76
Smith machine (90 degree angle, shoulder width stance) ----60
Biceps femoris (hamsring)
Standing leg curls --------------------------82%
Lying leg curls -----------------------------71
Seated leg curls ----------------------------58
Modified hamstring deads --------------------56
Semitendinosus (inner hamstring)
Seated leg curls ----------------------------88
Standing leg curls --------------------------79
Lying leg curls -----------------------------70
Modified hamstring deads --------------------63
Gastrocnemius (calf muscle)
Donkey raises -------------------------------80
Standing one-leg raises ---------------------79
Standing two-leg raises ---------------------68
Seated raises -------------------------------61
the book 'target bodybuilding' by per a tesch also has lots of scans done using MRI that proves that we can work/develop specific parts of the muscle, i.e. outer thigh, inner thigh, specific head of tri's, etc by changing the angle or exercise.
these MRI tests also agree/confirm bompa's and others aboves findings.