If there's one thing that really grinds my gears it's seeing people doing high intensity intervals and high rep, high volume training routines on reduced carbohydrate diets and expecting amazing results. Ironically its the default "get ripped quick strategy" largely in vogue. That's fine if you want really average results, accelerate the ageing process and generally look and feel haggard. If you want to look lean, fit and healthy you need to do things differently.
Whilst a discussion of every variation of low carb diet is outside the focus of this article there are several general advantages to lower carbohydrate approaches if done correctly. From an adherence and behavioural perspective they blunt your appetite making it easier to stay in a calorie deficit. For those prone to binging or who struggle to control their appetite this is the main benefit. Physiologically they improve insulin sensitivity and enhance your ability to mobilise stored body fat. For fat loss the potential is obvious but where most people tend to go wrong is training inappropriately.
The problem with high intensity intervals or any lactic acid inducing training for that matter is they are highly glycogen dependant activities."Great" you might be thinking, "I'll deplete all my muscle glycogen and burn even more fat." This is essentially the logic that's filtered down to the mainstream but like Chinese whispers it's not really correct. The benefits of glycogen depletion through training are only really effective if you plan on carb-cycling or re-introducing carbs into your diet, otherwise the benefits are transitory at best and dreadful at worst.
The secondary but possibly more important issue is that the byproduct of high levels of lactic acid is ammonia and significant amounts of free radical damage. Low carb diets exacerbate this issue because you're depriving yourself of the energy source that would normally buffer that damage. In fairness a moderate amount of lactic acid has a beneficial function but not in the way most people do intervals and met-con on low carb diets. What follows is rampant inflammation that can damage mitochondria and make you age way faster than you should. If you wanted to make yourself progressively weaker and older this is how to do it.
Assuming you're looking to make meaningful longterm changes in your health and appearance the thing you should be really doing is avoiding accumulating excessive lactic acid in your training when going low carb. If you really enjoy intervals or met-con either use them very sparingly or eat differently. Here's what you should be doing instead.
Firstly, cardiac output training should be your bread and butter for at least 6-8 weeks at a minimum. In non-nerd speak this means doing steady state cardio at a heart rate between 120-140 bpm for at least 90 minutes total a week - more is better. Most people will find 3 x 30 minutes doable and sufficient to induce the desired physical adaptations. Many folks can achieve that with a brisk walk so don't fret.
Boring as it may seem, the benefits of cardiac output training cannot be overstated and unlike other forms of training those benefits can be achieved reliably and those benefits tend to last a long time. It makes you better at utilising fat for energy, lowers blood pressure, lowers resting heart rate, will improve your libido and help you sleep better. So long as you push blood through your system at that rate for 6-8 weeks the positive structural adaptations in your heart, circulatory system and sympathetic tone are predictable. If there was a pill that could as consistently produce those benefits you'd be crawling over broken glass to get at it.
Importantly, cardiac output training will help balance out your nervous system on a lower carb eating plan. When you lower carbs and calories together your body starts producing more cortisol and adrenaline to mobilise energy. One of the common problems I see with low carbers following conventional fat loss advice is an inability to sleep and wind down, their bodies get jammed on fight or flight mode because they are essentially conditioning their body to constant stress. Cardiac output training can largely remedy that problem.
The second aspect to focus on is strength work. This advice can be applied to anyone but especially if you're low carb - get stronger in the 5-8 rep range on big compound exercises relative to your bodyweight. More advanced trainees might periodically go lower and heavier. Counterintuitive as it may seem you really want to stay away from "feeling the burn". Low volume, moderate reps, heavy weights relative to where you are at will do more to improve your physique than anything else when dietary carbs are low. Of course there are bodyweight training variations that can be used but for illustrative purposes I'll stick with familiar strength training.
As to frequency, if both calories and carbs are low, three days a week is plenty if you're training with intent. That said, I've gotten ridiculously lean on only two days per week. Regardless of frequency it's progress that is king, if you're not improving your lifts it's likely you're training too much. Most people - especially on low carb diets - are just training to feel tired, to actually look better you have to train to get better!
Learn to perform a handful of big, compound lifts with impeccable form for your body type and get stronger relative to your body weight. Apply that principle to your training and you will always get leaner - always, this isn't even up for debate. Training this way consistently is the fastest and most reliable way for the majority of people to achieve the sort of physique they're after. For females worried about getting big and bulky; it won't, it'll make you appear "toned" which really means low levels of body fat with appreciable muscle.
Not including warm ups and mobility a simple full body workout for a beginner/intermediate male trainee is below. The first three exercises are indicator exercises, these are the movements that are the biggest driver of progress. The rep goal for each movement is 8 reps, if you can't get 5 the weight it's too heavy. If the trainee is able to hit 8 reps on each set with three minutes rest, increase the weight fractionally the following week, if not it stays the same.
Squats 3 sets x 5-8 reps (Rest 3 minutes)
Incline Bench Press 3 sets x 5-8 reps (Rest 3 minutes)
Bent Over Row 3 sets x 5-8 reps (Rest 3 minutes)
Bulgarian Split Squat 3 sets x 5-8 reps (Rest 3 minutes)
Chin Up (palms facing) 3 sets x 5-8 reps (Rest 3 minutes)
Military Press 3 sets x 5-8 reps (Rest 3 minutes)
Dips 3 sets x 5-8 reps (Rest 3 minutes)
Romanian Deadlifts 3 sets x 5-8 reps (Rest 3 minutes)
Chest Supported Row 3 sets x 5-8 reps (Rest 3 minutes)