In short, YES!
The goals you mention of building muscle and burning fat are not mutually exclusive, biologically speaking if that is what you are asking. So in short yes your workout schedule can be effective but it may be a better strategy to prevent injury and maximize gains by having a rest period between weight days.
You know your schedule better that anyone but HIIT can also serve as a rest day for weight training so you could do HIIT on Wednesday and weights on Thursday. Just make sure that if your still very sore from your last wight day that you at least change up the workouts a bit to prevent injury.
Also, just how effective it is depends on a number of factors:
- Intensity & Sets/Reps
- Defining HIIT
The part that may be somewhat exclusive is the type of diet you adopt to target your specific goals.
As far as fat loss is concerned, diet play a very important role. Speaking generally, you'll need a diet that is lower in carbohydrates than the standard 65-75% macros that the USDA and WHO recommend (1,2) Recent studies have shown greater success with low carb vs low fat diets for reducing body fat and improving overall health. (3,4) How low you go on your carb intake depends on how much weight you want to lose and whether that or muscle gains are more important to you at the moment. Lowering carb intake will lead to better/easier results in fat loss but the tradeoff is that it will may negatively affect performance. In low carb diets protein synthesis can still work just as efficiently but maximum effort may be compromised. As such many people employ different strategies such as carb-cycling (5) to keep body fat as low as possible and performance high. Others have achieved slower but steady gains with diets such as the ketogenic diet. You'll have to find what works best for you but overall I'd suggest that you moderate your carb intake to achieve the best mix of muscle growth and fit appearance.
In either case, you will also want to increase your protein intake too, assuming you haven't already. The DRI (Dietary Reference Intake) is 0.8 grams of protein per kilogram of body weight, or 0.36 grams per pound. (6) While this meager amount is enough for a coma patient to prevent short term deficiency, most nutritionists advocate for at least .07 - 1 gram of protein per pound of lean mass for moderately to very active individuals. (7) Personally, I don't advocate for protein supplementation when you can get all the protein nutrients you need plus other nutrients from healthy and nutrient dense foods like fish, eggs, and, my favorite, steak. However, there is some research indicating that BCAA's can really help improve muscle recovery.
Intensity & Sets/Reps:
Strength and HIIT are great to use in conjunction to lower fat and increase strength. For anaerobic workouts the intensity of the lift is relative to one's skeletal muscular strength. This is why it is measured by lifting retaliative to x% of one's one Repetition Maximum (1RM). The higher the percentage, the higher the microtears to muscle and the greater the gains. Generally this is at 70-90% of 1RM. High percentage puts an extreme amount of strain and pressure on one's body.
This chart may vary for some but it gets you in the ballpark.
As shown in the chart, you'll need lower the overall reps to sets ratio with increased weight.
Not allowing your body time to conduct these repairs by adequate rest can lead to injury by damaging connective tissue, bones, or the muscles themselves by straining or tearing the muscle. There is a biological speed limit on growth and repair. Although it is not unheard of to injure a major muscle, it is more common to injure the smaller muscles supporting the joints involved in the lifts. For example, it is more likely that you'll injure your rotator cuff or shoulder when bench pressing as opposed to the pectoralis major/minor.
The soreness that you experience is one of the ways your muscles communicate to your body that they need rest. In this way, they "speak" for themselves. Although they can communicate with soreness, it is NOT an adequate indicator of muscle fatigue or to prevent injury. Heavy lifts above 75% of 1RM should be worked into gradually and should not be done by novices who have not properly preconditioned their body for stress and strain that ensue in heavy lifting. Proper from is very important so you do not put undue stress on your joints/back and connective tissues. If your unsure, stop, ask and/or research.
It is widely known that anaerobic resistance training stimulates Testosterone production in males and plays an important part in skeletal muscle growth and repair. (9,10) Testosterone accomplishes this by increasing the muscles' protein synthesis. As a result, muscle fibres become larger and repair faster with higher testosterone levels.
In summary, strength training with moderate to high intensity constellations (70-80% 1RM) multiple sets (3-5), short rest intervals (60-120s) and 8-12 repetitions lead to great hormonal responses. Besides mechanical stimuli, metabolic perturbations during strength training are discussed to have a great influence on the acute hormonal response and on gains in muscle strength and hypertrophy.
Source: Acute metabolic, hormonal, and psychological responses to strength training... -The German Research Center of Elite Sport, Cologne
Human Growth Hormone (HGH):
Human Growth Hormone (HGH) production is stimulated with anaerobic exercise activities and is naturally produced by the pituitary gland. (11) This hormone is responsible for the muscular and bone strength gains proceeding lifting and other exercises. HGH production varies throughout the day but most of it is produced during your sleep cycle. (12) HGH production will wane with age. (13) (See Chart Below) To both, maximize both your muscle and bone gains, you need to maximize HGH production. To maximize production of HGH, you'll need to get good rest (8 hours sleep) and enter into deep sleep as well as receive ample nutrition including protein and vitamins. (14,15,16)
A number of factors are known to affect GH secretion, such as age, sex, diet, exercise, stress, and other hormones. Sleep deprivation generally suppresses GH release, particularly after early adulthood. (13)
Some people supplement with BCAA's, Vitamin D, Glutamine, GABA, A-GPC, L-arginine and L-lysine to improve HGH production. Some suggest avoiding sugar after workouts or even entirely. They say that consuming sugar, especially fructose and sucrose because sucrose is broken into glucose and fructose, within 2 hours will cause your hypothalamus to release somatostatin, which will decrease your production of HGH. Simple sugars that are high-glycemic also spike insulin levels. Not only does this lead to body fat storage, but it severely decreases the release of growth hormone. (16) Refer to the chart below for additional information on inhibitors and inducers of HGH.
HIIT is great for fat loss and complements anaerobic workouts wonderfully but it is definitely not a replacement. HIIT is the perfect method for losing fat while retaining muscle mass. It is also a good way to train for spontaneous activities especially if you also desire to burn calories. Some people define HIIT differently, so I'll add this qualifier Weight training being -i.e. weighted squats, leg press, calf extensions, lunges, etc. and HIT being non-weighted High Intensity Workouts. Some HIIT techniques involve weighted exercise but they're employed with a different methodology. The focus with HIIT is to burn calories not to build muscle strength. One of the drawbacks of HIIT is that many of its activities may put you at risk of injury.
More on why HIIT is not a replacement for strength training:
“EMG techniques make it possible to study recruitment order, the relationship between stimulation and the amount of force developed, the type of muscle contraction (concentric vs. eccentric) and the effects of fatigue. EMG analysis in my study showed the approximate percentage of the recruitment of muscle fiber types in the quadriceps of a trained athlete during execution of a one repetition squat with progressively increasing loads.
Starting with 60% of one-repetition maximum, the slow-twitch fibers contribute 60 percent to the effort; fast-twitch fatigue resistant fibers, 30 percent; and fast-twitch fatigable 10 percent. At 100 percent maximum effort, however, the percentage of slow-twitch fibers involved is only 5%, while fast-twitch fatigue resistant is 15 percent, and fast-twitch fatigable is 80 percent.
The implications for athletic-type strength training are clear. To develop strength in the fast-twitch fibers you have to train with heavy weights. Light weights contribute little to optimizing strength and power performance.“
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