November 21, 2025

6 min read

30-Day Gym Challenge for Skinny Guys: Build Muscle & Gain 5kg

By Will Duru, BSc (Hons) Sport and Exercise Science, Award-winning Personal Trainer with over 10 years of experience in strength training and optimising recovery. 

Hello! I’m Will Duru. For almost a decade as a personal trainer in the City of London, my greatest passion has been helping people build muscle and transform their bodies. I’ve worked with everyone from busy professionals to guys just like you who feel like they’re doing everything right but still struggling to put on size. If you feel like you’re a “hardgainer” or just can’t seem to build the physique you want, this challenge is for you. This is your 30-day blueprint to pack on serious muscle, build strength, and finally see the results you deserve.

The Ultimate 5-Day Training Split for Muscle Growth (How I Gained 8kg of Muscle)

You Are Not a "Hardgainer" - You Just Need the Right Plan

The two biggest mistakes skinny guys make are not training with enough intensity and, most importantly, not eating enough food. Your body needs two things to grow: a reason to build muscle (intense strength training) and the fuel to build it with (a calorie surplus). This program provides both. We will use a proven Push/Pull/Legs split combined with progressive overload to force your muscles to grow, and I’ll give you the exact nutritional strategy to fuel that growth [1].

30-Day Dumbbell Strength Challenge: The Ultimate Home Workout Plan

The Non-Negotiable Warm-Up (15 Minutes)

Never skip your warm-up. It’s essential for preventing injury and preparing your body for the work ahead. Perform this routine before every single workout.

Movement

Duration/Reps

Focus

Cardio

5 minutes

Light jog, cycling, or rowing to increase heart rate

Mobility

 

 

Cat-Cow Stretch

10 reps

Spine mobility

Thoracic Spine Windmills

10 reps/side

Upper back rotation

World’s Greatest Stretch

5 reps/side

Full body mobility (hips, spine, shoulders)

Activation

 

 

Banded Glute Bridges

15 reps

Activate glutes

Band Pull-Aparts

15 reps

Activate upper back and shoulders

Bodyweight Squats

15 reps

Activate lower body

Your 30-Day Gym Calendar

Week

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Day 7

All Weeks

Push Day

Pull Day

Legs & Core

Push Day 2

Pull Day 2

Active Rest

Rest

strength training app- 12reps app - personalised strength training

The Complete 4-Week Workout Program

Week 1: Building the Foundation

Focus on perfect form. The weight should be challenging, but you must complete all reps.

Day 1: Push

Exercise

Sets

Reps

Rest

Barbell Bench Press

4

8-10

90s

Incline Dumbbell Press

4

8-10

60s

Dumbbell Shoulder Press

4

8-10

60s

Lateral Raises

4

12-15

45s

Cable Tricep Pushdown

4

10-12

45s

Overhead Tricep Extension

4

10-12

45s

Day 2: Pull

Exercise

Sets

Reps

Rest

Deadlifts

4

5-8

120s

Lat Pulldown

4

8-10

60s

Seated Cable Row

4

8-10

60s

Face Pulls

4

15-20

45s

Barbell Bicep Curls

4

10-12

45s

Hammer Curls

4

10-12

45s

Day 3: Legs & Core

Exercise

Sets

Reps

Rest

Barbell Back Squat

4

8-10

90s

Romanian Deadlifts

4

10-12

60s

Leg Press

4

10-12

60s

Leg Curls

4

12-15

45s

Hanging Knee Raises

4

To Failure

45s

Cable Crunches

4

15-20

45s

Day 4: Push Day 2

Exercise

Sets

Reps

Rest

Barbell Bench Press

4

8-10

90s

Incline Dumbbell Press

4

8-10

60s

Dumbbell Shoulder Press

4

8-10

60s

Lateral Raises

4

12-15

45s

Cable Tricep Pushdown

4

10-12

45s

Overhead Tricep Extension

4

10-12

45s

Day 5: Pull Day 2

Exercise

Sets

Reps

Rest

Deadlifts

4

5-8

120s

Lat Pulldown

4

8-10

60s

Seated Cable Row

4

8-10

60s

Face Pulls

4

15-20

45s

Barbell Bicep Curls

4

10-12

45s

Hammer Curls

4

10-12

45s

strength training app

Week 2: Increasing Volume

We add one extra exercise to each day to increase the total workload.

Day 1: Push

Exercise

Sets

Reps

Rest

Barbell Bench Press

4

8-10

90s

Incline Dumbbell Press

4

8-10

60s

Dumbbell Shoulder Press

4

8-10

60s

Lateral Raises

4

12-15

45s

Cable Flys

4

12-15

45s

Cable Tricep Pushdown

4

10-12

45s

Overhead Tricep Extension

4

10-12

45s

Day 2: Pull

Exercise

Sets

Reps

Rest

Deadlifts

4

5-8

120s

Lat Pulldown

4

8-10

60s

Seated Cable Row

4

8-10

60s

Single-Arm Dumbbell Row

4

10-12/arm

60s

Face Pulls

4

15-20

45s

Barbell Bicep Curls

4

10-12

45s

Hammer Curls

4

10-12

45s

Day 3: Legs & Core

Exercise

Sets

Reps

Rest

Barbell Back Squat

4

8-10

90s

Romanian Deadlifts

4

10-12

60s

Leg Press

4

10-12

60s

Leg Curls

4

12-15

45s

Calf Raises

4

15-20

45s

Hanging Knee Raises

4

To Failure

45s

Cable Crunches

4

15-20

45s

Day 4: Push Day 2

Exercise

Sets

Reps

Rest

Barbell Bench Press

4

8-10

90s

Incline Dumbbell Press

4

8-10

60s

Dumbbell Shoulder Press

4

8-10

60s

Lateral Raises

4

12-15

45s

Cable Flys

4

12-15

45s

Cable Tricep Pushdown

4

10-12

45s

Overhead Tricep Extension

4

10-12

45s

Day 5: Pull Day 2

Exercise

Sets

Reps

Rest

Deadlifts

4

5-8

120s

Lat Pulldown

4

8-10

60s

Seated Cable Row

4

8-10

60s

Single-Arm Dumbbell Row

4

10-12/arm

60s

Face Pulls

4

15-20

45s

Barbell Bicep Curls

4

10-12

45s

Hammer Curls

4

10-12

45s

strength training app- 12reps app - personalised strength training

Week 3: Increasing Intensity with Supersets

Perform exercises 1A & 1B back-to-back with no rest. This is a huge intensity jump.

Day 1: Push (Supersets)

Exercise

Sets

Reps

Rest

1A. Barbell Bench Press

4

8-10

0s

1B. Incline Dumbbell Press

4

8-10

90s

2A. Dumbbell Shoulder Press

4

8-10

0s

2B. Lateral Raises

4

12-15

60s

3A. Cable Tricep Pushdown

4

10-12

0s

3B. Overhead Tricep Extension

4

10-12

60s


Days 2-5: Follow the same superset structure as Week 2, pairing exercises together.

strength training app 12reps app

Week 4: Peak Week with Dropsets

On the final set of the first exercise of each day, perform a dropset: immediately reduce the weight by 20-30% and perform as many more reps as possible (AMRAP).

Follow Week 3 structure for all days, adding dropsets to the first exercise of each workout.

30-Day Dumbbell Strength Challenge: The Ultimate Home Workout Plan (Dumbbell Only)

Nutrition: You Must Eat to Grow

This is the most critical part. To gain 5kg of lean muscle, you must be in a calorie surplus. For a 65kg guy, that means eating around 2,900 calories per day. Here are your target macros for clean bulking:

  • Protein: 130g (The building blocks of muscle [2])
  • Fat: 80g (Essential for hormone production)
  • Carbohydrates: 414g (Your primary energy source for intense workouts)

Use MyFitnessPal to track every single thing you eat. Be meticulous. If you are not gaining weight, you are not eating enough. Slowly increase your carbs and fats until you are gaining 0.25-0.5kg per week.

Supplements for Hardgainers

  • Creatine: 5 grams daily. It’s the most proven supplement for increasing strength and muscle mass [3].
  • Whey Protein: One or two scoops daily to easily hit your protein target [2].

Use the 12Reps App as Your Digital Logbook

This entire 4-week plan is your new bible. Build it in the 12Reps app to stay accountable.

  • Build Your Routine: Input every workout for all 4 weeks
  • Track Your Lifts: Log your weights and reps for every exercise. If you aren’t getting stronger, you aren’t growing
  • Use the Stopwatch: Keep your rest periods strict. No excuses

Download the app, get your free trial, and let’s get to work.

strength training app - 12reps app

Conclusion: Your Transformation Starts Now

You now have everything you need to transform from skinny to strong in the next 30 days. This is not just a workout program. This is your roadmap to building the body you have always wanted. The weights, the sets, the reps, and the rest periods are all laid out for you. The nutrition plan is clear. The warm-up routine is ready. All you need to do is commit.

Remember, building muscle is not magic. It is science. You need to train hard, eat more than you think you need, and stay consistent. The first week will feel challenging. The second week will feel harder. By week three, you will start to feel stronger. By week four, you will see the changes in the mirror. That is when you will realize that you are not a hardgainer. You just needed the right plan.

Track every single workout in the 12Reps app. Log your weights. Watch the numbers go up. That is your proof that you are growing. Take progress photos every week. Weigh yourself every morning. The scale should be moving up by 0.25-0.5kg per week. If it is not, eat more.

This is your time. Stop making excuses. Stop saying you have bad genetics. Stop blaming your metabolism. Start eating. Start lifting. Start growing. I have seen hundreds of guys just like you pack on serious muscle with this exact approach. You can do this. The only question is: will you?

Let’s get to work. Download the 12Reps app, build your routine, and start your transformation today. conculsion 

References

[1] Westcott, W. L. (2012). Resistance training is medicine: effects of strength training on health. Current sports medicine reports, 11(4), 209–216. https://pubmed.ncbi.nlm.nih.gov/22777332/

[2] Park, Y., et al. (2019). Effects of whey protein supplementation prior to, and following, resistance exercise on body composition and training responses. Journal of Exercise Nutrition & Biochemistry, 23(2), 34–44. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6651693/

[3] Mills, S., et al. (2020). Effects of Creatine Supplementation during Resistance Training Sessions in Physically Active Young Adults. Nutrients, 12(6), 1880. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7353308/

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12Reps Team

The 12reps app is your ultimate fitness companion, crafting tailored workout plans, tracking your progress, and keeping you motivated every step of the way. Whether you’re at home, in the gym, or on the go, our adaptable approach fits seamlessly into your lifestyle — providing the support and guidance you need to crush your goals and stay on track.

Disclaimer: The ideas in this blog post are not medical advice. They shouldn’t be used for diagnosing, treating, or preventing any health problems. Always check with your doctor before changing your diet, sleep habits, daily activities, or exercise.  JUST12REP.COM  isn’t responsible for any injuries or harm from the suggestions, opinions, or tips in this article.

30-Day Dumbbell Strength Challenge | Full-Body Workout Plan
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