I have a fairly reputable yoga instructor with 16 years of experience in various fitness-related roles who claims that increasing range of motion through stretching actually reduces stability. The reasoning is that having looser muscles can actually make you weaker to some degree and even reduce explosive strength. However, after looking through many documented research papers, I have not found any evidence to support this claim.
Excessive joint mobility and muscle flexibility can cause instability and lack of strength at end ranges of motion. Most people need to improve their range of motion because they are so immobile. But for people who are extremely mobile, pushing to further ranges of motion can cause problems.
For many sports, tasks, and health in general, we want to maintain some level of mobility, but not too much, especially in some areas. For instance:
The chances of injuries are high whenever stability is sacrificed at the expense of excessive mobility because parts of the body structures that should be stable (such as the lower back) are not.
Or consider the shoulder. It is an extremely mobile joint, and too much flexibility in the musculature of the shoulder can impede maintaining stability.
Or, your instruction may also be referring to the short-term decrease in power output that comes with static stretching: if you stretch for instance your hamstrings deeply, you won't be able to sprint as fast in the same workout. Explosiveness is reduced at end ranges of motion both from lack of strength and automatic inhibitory effects.
"The reasoning is that having looser muscles can actually make you weaker to some degree and even reduce explosive strength."
This is simply not true. Flexible, and loose are 2 different thing. Flexible means how easily your parts move away from the zero potential, and back. A loaded spring is flexible, but does it lose it's explosive power? No.
If you ask me for an example, I'd suggest check the person named "Elliot Hulse". He believes in the importance of range of motion to avoid injury and increase muscle memory. He won a strong man competition in 2009 where you need explosive strength as well as flexibility, especially while moving those atlas stones.
So, you'll be fine. I'd say full range of motion would rather do you good. After all, you wouldn't like to have a body that's too rigid to even move.
First of there is a medical condition called hypermobility . So yes to much mobility is not a good thing.
Regarding the effects of stretching on strength I found these papers:
"Maximal strength decreased after static stretching (213.2 6 36.1 to 184.6 6 28.9 kg), but it was unaffected by ballistic stretching (208.4 6 34.8 kg). In addition, static stretching exercises produce a greater acute improvement in flexibility compared with ballistic stretching exercises. Consequently, static stretching may not be recommended before athletic events or physical activities that require high levels of force. On the other hand, ballistic stretching could be more appropriate because it seems less likely to decrease maximal strength."
Bacurau et al. Acute effect of a ballistic and a static stretching exercise bout on flexibility and maximal strength. Journal of Strength and Conditioning Research (Impact Factor: 2.34). 2009. 240 citations.
"However, there are a myriad of studies demonstrating static stretch-induced performance impairments. More recently, there are a substantial number of articles with no detrimental effects associated with prior static stretching."
A review of the acute effects of static and dynamic stretching on performance. European Journal of Applied Physiology. (Impact factor: 3.055). 2011. 208 citations.
"On the basis of the current evidence, the inclusion of short durations of either static or dynamic stretching is unlikely to affect sprint running, jumping, or change of direction performance when performed as part of a comprehensive physical preparation routine."
Blazevich et al. No Effect of Muscle Stretching Within a Full, Dynamic Warm-up on Athletic Performance. Medicine & Science in Sports & Exercise (Impact factor: 4.29). 2018. 20 citations.
So it seems that it was earlier found that static stretching reduced maximal strength whereas ballistic did not. More recently it has been found that static stretching does not reduce strength.
One problematic (?) thing I notice with (1) and (3) are the low number of subjects: n=14 and 20. Furthermore (1) only included women and (3) only men.
This seems to indicate a problem with low quality in sport science papers?
(2) Is a metastudy and should therefore probably be given most weight. It also proposes some reasons for the conflicting findings: "The lack of impairment may be related to a number of factors. These include static stretching that is of short duration (<90 s total) with a stretch intensity less than the point of discomfort. Other factors include the type of performance test measured and implemented on an elite athletic or trained middle aged population. Static stretching may actually provide benefits in some cases such as slower velocity eccentric contractions, and contractions of a more prolonged duration or stretch-shortening cycle. Dynamic stretching has been shown to either have no effect or may augment subsequent performance, especially if the duration of the dynamic stretching is prolonged."
Dynamic stretching does not affect strength. Mild static stretching probably does not affect strength.
According to this article: Stretching: Focus on flexibility "other studies show that lengthening the muscle and holding the stretch immediately before a sprint may slightly worsen performance."
Is actually the opposite.
With increased health of the fascia you will actually get a structure called CRIMP that is found in young and healthy connective tissue.
This will garant an optimal transmission of kinetic energy through the muscular-skeletal structure and improve your stability.
When you stretch you do not act only on the myofibrils, but the part of the muscle you modify is the cytoskeleton ( intended as the whole structure ) and the connective tissue ( comprising of tendons ).