Regular weight training for strength and power should not make you sore, and shouldn’t negatively impact subsequent Muay Thai training. If you’re repeatedly getting sore following your weight training, you’re doing something wrong. Athletic strength and conditioning training should complement your Muay Thai not contend with it.
When trained correctly, strength and power training fatigues the neuro-muscular system (central nervous system) rather than causing soreness through damage to the structural system (muscle fibres). Think of neuro-muscular fatigue as frying your wiring, temporarily increasing its resistance and inhibiting spark transmission along your nervous system which fires muscle contraction. My article on timing training to boost recovery and performance explains how neuro-muscular fatigue lasts between 12 to 36 hours depending on the intensity and volume of your strength and power training, whereas structural fatigue can last between 1 to 3 days.
This is another reason why training for aesthetic hypertrophy (increased muscle mass) like a body builder is not desirable for a fighter. The objective of hypertrophy training is to damage muscle fibres so that they repair larger and better able to cope with the load and volume of this specific type of work. This will make you sore, and therefore interferes with your technical and tactical Muay Thai training — not to mention increase body mass without a proportional strength increase, resulting in decreased athletic performance.
There is a place for functional hypertrophy in a fighters programme if a particular fighter requires it. But the focus is on growing muscles that drive athletic movement with a complimentary strength increase, not just muscles for show. Even so, expect some soreness during this training phase. For an example of a functional hypertrophy routine for Muay Thai, take a look at the following article:
TO AVOID SORENESS (STRUCTURAL DAMAGE)
Weight training for strength and power should use compound movements (not isolated joints) and be conducted at high intensity and low volume; typically 3–5 sets of with a load you can only lift for 1–5 reps. This is neuro-muscular training without the structural damage and associated soreness. More on this in the following two articles:
Don’t suddenly increase exercise volume or intensity. Progressive overload is the key to not only avoiding unwanted structural damage, but also long term progression. Here’s a couple of articles going into more detail regarding this:
Don’t overdo the eccentric movements (where muscles lengthen under load), they make you sore! Lowering a weight super-slowly during weight training falls into this category, as does a sudden increase in volume of lunges, plyometric jumps, clap pushup etc. Make sure you progressively introduce such movements as they’ll inevitably result in delayed onset muscle soreness (DOMS). More on this in the following article:
Generally, any new movement can make you sore because your body hasn’t yet adapted to it. Just because you’re experienced in some exercises, don’t assume this carries over into new ones. Be prepared to build intensity and volume of unaccustomed movements, because they may work your body through a new range of motion, involve a more intense load or greater volume. Check out my Training Age article for more of a perspective on this.
A little soreness following training is ok, as long as it doesn’t affect skilled movement patterns. Crippling soreness and stiffness is not good (despite being a badge of honour for the uninitiated), it doesn’t mean you had a great session, it means you messed up your planning!