When you pick up a barbell or a pair of dumbbells or resistance bands, your focus turns to building muscle and making the muscles you’re working stronger, but muscles aren’t the only tissues that are transformed by weight training. Weight training also impacts tissues that support your body and protect it from injury. What are these tissues? Bones and connective tissue, of course. Have you ever thought about how these structural components respond to resistance training? Let’s find out.
How Weight Training Changes Connective Tissue
You depend on healthy connective tissue to protect you from injury when you work out. In fact, for some people, connective tissue can be the “weak link” that limits their performance and places them at higher risk for injury. Connective tissue is made up of cells and fibers, mostly collagen fibers, in a gelatinous matrix. Its primary function is to support structures inside your body. With regards to weight training, the connective tissues we’re most focused on are tendons and ligaments.
Tendons are connective tissues that attach muscle to bone. When muscles contract the dense, fibrous tendon pulls on the bone and causes the bone to move. If you’ve ever had a tendon injury, you know how painful they can be and how slowly they heal. Ligaments are connective tissue that connect one bone to another and help stabilize joints. Unlike tendons that are typically very dense and fibrous, ligaments are relatively thin and have varying degrees of elastic tissue that give your joints flexibility.
Healthy tendons are strong and capable of generating a great deal of power. Unfortunately, tendons are also prone to injury, and when they’re injured it can take months for them to heal. During that time, the muscle that connects to the tendon atrophies because you can’t work the muscle. As a result, you lose muscle mass. That’s why it’s so important to keep tendons healthy.
So we know healthy tendons and ligaments are important, but how do these tissues respond to resistance training? Can you make connective tissue stronger and more impervious to injury? Based on a limited amount of research, it appears that tendons and ligaments CAN become larger and stronger in response to resistance training. When you overload a muscle through resistance training, protein synthesis goes up in response. Connective tissue responds to training in a similar way by increasing the number of collagen fibers inside the matrix of the connective tissue. Since muscle also contains connective tissue, the expansion of collagen accounts for some of the hypertrophy a muscle undergoes in response to training.
The degree to which connective tissue grows and becomes stronger is proportional to how much the muscle is overloaded. There seems to be a threshold level of exercise needed to boost connective tissue growth. Lifting very light weights is usually not enough – you have to sufficiently stress the muscle by overloading it.
Where does the growth take place? The connective tissue fascia that surrounds the muscle can increase in size and connective tissue growth can occur within the tendon itself. It makes sense that connective tissue growth would mirror that of the muscle since you need strong collagen to support a developing muscle.
Bone Health: How Your Bones Respond to Resistance Training
Did you know bone is also a type of calcified connective tissue? Just as tendons and ligaments can grow in response to resistance training, so does bone. That’s important when you consider that you lose bone tissue every decade after 30. When muscles pull on tendons, the force is transmitted to the bone. This generates a stimulus for new bone formation, assuming the load placed on the muscle is great enough. As mentioned, bone won’t grow in response to a light load – there’s a threshold stimulus needed to stimulate bone growth called the minimal essential strain. When the load placed on the bone is greater than this amount, new bone is laid down.
How heavy do you have to lift to stimulate bone growth? It depends on your level of training. For a sedentary, untrained person brisk walking or relatively light weight training may be enough. However, better-trained individuals generally need high-intensity, weight-bearing exercise or to lift heavy weights to stimulate bone growth. In fact, research suggests trained individuals need to train with a resistance of 80 to 90% of one-rep max to encourage bone growth.
Overall, research shows the best forms of exercise for stimulating bone growth are heavy resistance training and high-impact exercise such as plyometrics and running. Non-weight bearing exercises like swimming have little or no effect on bone density. As you might expect, compound exercises that work more than one muscle and joint provide the greatest stimulus for bone development. Squats, deadlifts, and lunges using heavy resistance stimulates bone growth in the femurs but has little effect on bones in your arms and wrists. Overhead presses and bench presses are more effective for building bone mass in the arms. High-impact exercise such as running and jumping best target the bones in your spine and hips.
Be sure you’re following the principle of progressive overload. Just as your muscles adapt to a stimulus over time, your bones do too. So you have to increase the load you place on your muscles/bones to continue to boost bone growth.
Keep in mind that after early adulthood, you won’t experience a large increase in bone density even with exercise, but high-impact exercise and resistance training help reduce age-related bone loss and strengthen the muscles that overly the bone. Don’t forget to talk to your doctor about when to get a bone density study to make sure you’re not experiencing significant bone loss. You may not experience signs and symptoms until you experience your first fracture. Risk factors for osteoporosis include:
Low body weight or BMI
Having a small frame
Heavy use of alcohol
History of an eating disorder like anorexia nervosa
Consuming a diet low in calcium
The Bottom Line
When you resistance train regularly, you become stronger and improve your body composition. In addition, you strengthen the connective tissue that surrounds your muscles and bones as well as your bones. With so many benefits of resistance training, how can you afford not to do it?
ACSM Current Comment. “Resistance Training and Injury Prevention”
Med Sci Sports Exerc. 1988 Oct;20(5 Suppl): S162-8.
Essentials of Strength Training and Conditioning. Second edition. Baechle and Earle. (2000)
Med Sci Sports Exerc. 1999 Jan;31(1):25-30.
Sports Med. 2009;39(6):439-68. doi: 10.2165/00007256-200939060-00002.
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