One thing that will aid your question getting answered is trying to make them as interesting as possible, as I am more inclined to spend time answering a thought provoking, interesting or well asked question than the usual 'I want a big chest, washboard abs - what exercises and nutrition plan should I use'.
Sorry but that kind of question is too vague and just doesn't give me enough information about you as well it shows that you have not bothered to use any of the information presented on this site and the countless others to at least do a bit on your own in terms of research. Now that has been said lets get on with the Edification from across the pond:
[ Q ] My training partner has been raving about a technique in which each rep is performed with a different speed (i.e. one rep takes six seconds to complete and is slow and controlled and the next is explosive and only takes a second or so). Do you see any benefits to this?
The technique you mention is fairly useful for developing hypertrophy in the fast twitch fibres, which would not usually be called into play with standard controlled rep cadence training (i.e. two seconds up, two to four seconds down).
This occurs as slower reps taking in the range of six to twelve seconds will fatigue the intermediate and possible fast twitch fibres (if the weight is heavy enough) that have an endurance time under this time period.
Upon commencement of an explosive rep the fast twitch and intermediate fibres should be recruited, however the last rep fatigued them and as such a special population of fast twitch fibres used exclusively for ballistic movements will be recruited instead. This population of fast twitch fibres has been shown to be recruited during times of fatigue, coupled with the explosive rep you should be able to exhaust these and see new growth.
Here is a quick and easy variation of this using dumbell squats.
Stand feet just beyond shoulder width with feet slightly turned out with a set of dumbells in either hand. Taking four seconds lower yourself down into a squat position. Hold at the midpoint for four seconds (should be at parallel) and slowly rise up for four seconds. Once at the top drop straight back down into the squat position and explode back up using enough force to leave the ground. Upon landing repeat the sequence of a slow rep followed by a fast rep for five sequences or ten total reps.
Another factor which makes this a great technique is that your total Time Under Load (TUL) is increased which results in more metabolic work and therefore more byproducts which can act as chemical signals for growth and release of growth factors. More importantly is that it teaches control and takes away the repetitiveness of just cranking out reps. This kind of variation in rep cadence is great for finishing of a workout (well if your masochistic) but for best recruitment of the fast twitch fibres it should be done earlier on.
[ Q ] You always seem to promote a varied rep range to promote hypertrophy. However a guy at my gym states that sets of eight to twelve reps promote hypertrophy and reps lower than this only build strength and reps higher only develop endurance. I'm confused, who's correct?
The guy is right that sets of eight to twelve are better for increasing myofibril hypertrophy. The reason being relates to the amount of protein degradation generated by lifting weights (the heavier the weight the greater the degradation) coupled with the total mechanical work.
Heavy maximal strength training with low reps produces large amounts of protein degradation per lift but because the total mechanical workload is low the net protein degradation is also low. Inversely high rep training (especially above twenty reps) produces very low levels of protein degradation even though the mechanical workload is high and again net protein degradation is low.
Training with moderate rep ranges (between six and fifteen) provides a compromise in that protein degradation is moderately high and mechanical workload also remains elevated with a resultant net protein degradation greater than either low or high rep training. The consequence is greater myofibril hypertrophy.
Now this is not to say that high or low rep training doesn't produce myofibril hypertrophy they do (especially if the trainee is unaccustomed to it).
The truth is a muscle is a multifaceted structure and is composed of more than just protein. Both high low rep training will develop all the components that lend themselves to growth (myofibril and sarcoplamsic hypertrophy, capillarisation and connective tissue alterations) as well as providing increases in physical capacity (force production, substrate storage etc) that will enable higher workloads during traditional bodybuilding style training.
Obviously if your goal is putting on muscle mass the majority of your training should be focused on myofibril hypertrophy style training (i.e. moderate reps), but for maximal development a proportion of your time should also involve higher rep and lower rep work.
[ Q ] A trainer at my gym says that I should change exercises every six weeks. Do you think this is necessary or even beneficial?
To a degree yes, in order for muscular improvements there has to be a constantly changing stimulus or else the muscles would have no reason to adapt and change. Now having said that, do I believe that you need to change exercises every six weeks? In short a big fat no!
The 'familiarity' of an exercise is just one variable that will cause an adaptive response from the muscles. The reason a new exercise creates new growth is through the different recruitment patterns of the motor units. During certain motor patterns (movements or exercises) the muscle fibres and their control network (termed motor units) are recruited in specific orders.
Studies have shown that different movements recruit the motor units in different orders. This means different muscle fibres get exhausted which don't usually. As such it's easy to see that new movements will spur new growth.
However the initial strength gains seen when doing new exercises are purely neurological. Your body is probably the most conservative machine out there and will do the least amount possible in terms of adaptation to overcome new stressors (that's why our ancestors managed to survive during times of hardship). As such the initial strength gains seen doing new exercises is just the result of increased coordination of the neurological capabilities of the muscle (i.e. inter-muscular coordination).
This is pretty much the same as when some one first starts weight training - loads of strength increases the first six weeks - not many physical changes. Not exactly what you want when trying to pack on mass.
This is why I personally recommend changing the exercises only once other avenues for change and progression have been exhausted. There is around five avenues for progressive overload - increased intensity (weight used), increased volume (sets and reps), increased density (decreased rest time), increased frequency the body part is trained and finally familiarity.
For a guide to using these entire avenues see my article 'means to mass', where a sample basic bodybuilding periodised structure is presented.
That's it for this installment of Edification from across the pond, until next time train hard but even better train smart.