Health Claims

If untrained adult men lift weights twice a week for 8 weeks, doing 4-6 sets of 8-12 reps until they can't do any more, their upper arm muscles will get bigger - this is measurable with ultrasound or other imaging.

Causal

When untrained adults want bigger biceps, doing simple curl exercises works better than doing rows that use multiple muscles at once.

Causal

When you do a particular exercise, you get stronger mainly in the muscles you used to do that exercise - not necessarily in other muscles.

Causal

Doing bicep curls leads to bigger arm muscles (11% growth) than doing dumbbell rows (5% growth) after training for 8 weeks, at least in men who haven't exercised before.

Quantitative

If you want bigger biceps, you should focus on exercises that only move your elbow (like bicep curls) instead of exercises that involve multiple joints (like pull-ups).

Causal

When you do exercises that work multiple muscle groups at once (like rowing), you get better at other multi-joint movements. When you do exercises that only work one joint (like bicep curls), you mainly get better at single-joint movements.

Causal

When untrained men do arm curls for 8 weeks, their biceps get thicker (about 11%). But when they do dumbbell rows instead, their biceps only grow about half as much (about 5%).

Quantitative

Scientists aren't sure if the temporary muscle puffiness you get after working out is a good sign that your muscles will actually grow bigger over time. It might work for some muscle groups but not others, so we need more studies to figure this out.

Correlational

Doing both compound movements like pull-ups and isolation exercises like dumbbell curls is the best way to build bigger biceps and the underlying brachialis muscle.

Causal

Just because a workout makes your muscles feel huge and pumped during the session doesn't guarantee they'll actually grow bigger over time.

Correlational

When you lift weights for a long time, some muscles like your chest can grow bigger than they do right after a workout, but this doesn't happen with your arm muscles like biceps.

Correlational

Your muscles can actually swell up bigger right after just one workout than they do after training consistently for several weeks.

Quantitative

Can doing lat pulldowns (a back exercise where you pull a bar down) build your biceps just as much as doing regular barbell curls? This claim says yes - for people who are new to working out.

Quantitative

When you work out, different parts of the same muscle can grow at different rates. Some exercises might make the far ends of your muscles grow more than the middle parts.

Descriptive

When you lift weights and your muscles get bigger temporarily (that's called the 'pump'), that doesn't actually tell you if your muscles will grow bigger for real over time. Scientists found that muscles that swell a lot right after exercise don't always end up growing the most.

Correlational

When you do bicep curls (an isolation exercise), your muscles get a bigger 'pump' right after compared to doing rows (a compound exercise), especially near the top of your arm close to your shoulder.

Quantitative

When you do compound exercises like dumbbell rows that work multiple muscles at once, they might build muscle in some parts of your arm about the same as isolation exercises like dumbbell curls that focus on just one muscle. But in other parts of your arm, the two types of exercises might build muscle differently.

Quantitative

When young women want to strengthen their soleus muscle (the lower calf muscle), doing calf raises with bent knees works better than doing them with straight legs.

Causal

For young women who want to work all three muscles in their calf (the two parts of the gastrocnemius and the soleus), doing calf raises with straight legs works better than doing them with bent knees.

Causal

When young women do calf raise exercises until they can't do any more, doing them with bent legs makes the calf muscle grow about twice as much as doing them with straight legs.

Quantitative

When young women do calf raises until they can't do any more, doing them with straight legs makes the outer calf muscle grow about twice as much as doing them with bent knees.

Quantitative

When young women do calf raises until they can't do any more, doing them with straight legs makes the upper calf muscle grow way more than doing them with bent knees (+8.8% vs -0.9%).

Quantitative

When you change the angle of the bench press, it might make the different parts of your chest muscle work in uneven ways, potentially causing one part to activate differently than the other.

Correlational

Scientists can use two tools together - one that measures muscle electrical activity and another that takes wide ultrasound pictures - to see how specific parts of the chest muscle change right after working out.

Descriptive