Free weights and machines

What it is

Two ways to add weight

A 2023 systematic review, which searches for the research on a question in a set, checkable way, set out the two kinds¹. Free weights often means exercises done with dumbbells and barbells¹. A machine can be defined as a device that holds a pin-loaded stack of weights¹.

The same review describes how they differ in movement¹. Most machines guide the weight along a set path in one fixed plane¹. That lowers the work asked of synergists, muscles that help another make the same movement¹. With free weights, the lifter usually sets the path more freely¹.

Two designs of machine are described in the studies^2,3:

• The Smith machine. A 2005 study describes it as a bar that moves up and down on a fixed vertical path, unlike a free weight².
• Cam machines. The authors of a 2020 trial note that some machines use a cam (a shaped, off-centre pulley)³. The cam better matches the strength curve, how much force a muscle can make through the range of motion³.

Powerlifting and weightlifting

Powerlifting has three competition lifts: the squat, the bench press and the deadlift⁴. Olympic weightlifting has two: the snatch and the clean and jerk⁴. Powerlifting uses higher top loads for body weight and centres on maximal force⁴. Weightlifting moves are faster, cover a larger range of motion and centre on producing force quickly⁴.

Variations of the weightlifting lifts, such as the hang clean and power snatch, are widely used to train qualities that underpin other sports⁵. A 2015 review describes pulling variations, such as the clean pull and jump shrug⁶. These leave out the catch (the part of a lift where the lifter receives the bar)⁶. The review calls these pulls less complex technically than the full lifts⁶.

What it loads

Balance against force

The 2023 review states that free weights call for more coordination between muscles, because the movement is less stable¹. In lifts such as the squat and bench press, this can come with more electrical activity in the synergists¹. The review notes that some studies found more weight could be lifted on a machine in a similar movement, such as the Smith machine squat¹. The review suggests muscles may put stability ahead of force when stability demands rise¹.

The review also speculates that machines may make it easier to single out one muscle group¹. In free-weight lifts such as the front squat, the trunk muscles could limit what the lifter can do¹. A 2010 Canadian position stand states that ground-based free-weight lifts, such as squats and deadlifts, can match or exceed core muscle activity on unstable surfaces⁷.

What small lab studies measured

The squat study measured electrical activity in the muscles, as electromyography does by picking up their signals⁸. In one study, the squat and bench press results pointed opposite ways²:

Comparison	What was found
Free-weight vs Smith squat, 6 people	Higher activity in the gastrocnemius (large calf muscle), biceps femoris (a hamstring muscle) and vastus medialis (inner thigh quadriceps muscle) with free weights8
Same study, four other muscles	No significant difference in four muscles, including the lumbar (lower back) erector spinae (long back muscles)8. Averaged over the seven muscles, free-weight activity was 43% higher8
Chest press, 12 resistance-trained men	Pectoralis major (large chest muscle) and anterior deltoid (front of the shoulder) activity did not differ across Smith machine, barbell and dumbbells9. Biceps brachii (front upper-arm muscle) activity rose as stability demand rose9
Heaviest single lift, 16 men and 16 women	More weight in the Smith squat than the free squat, significant in the women only2. More in the free bench press than the Smith bench press2
Bent-over row, 15 resistance-trained men	More erector spinae activity with the free-weight row than the machine row10
Overhead press, 8 competitive bodybuilders	The authors concluded the barbell press excites the muscles more than a machine press11
Hip abduction, 11 men	Gluteus medius (a buttock muscle) activity did not differ between a hip abductor machine, side-lying hip abduction and the clamshell12

In the chest press study, the heaviest single lift with dumbbells was 14% below the Smith machine and 17% below the barbell⁹.

The 2023 review adds a caution¹. The link between muscle activity in one session and long-term growth is uncertain¹. So higher synergist activity with free weights does not by itself show that they build more muscle¹.

How the body adapts

Both kinds build strength and muscle

A review of trials in healthy adults found every resistance training plan it examined beat no exercise for strength and muscle size¹³. A 2023 meta-analysis pooled 13 studies of 1016 adults aged 18 to 60 that compared free weights with machines¹. Free-weight groups mostly did barbell lifts, for example bench presses and back squats¹. Machine groups mostly did the leg press, chest press and Smith machine exercises¹. Both kinds significantly raised maximal strength, isometric strength, jump height and muscle size¹.

Gains follow the equipment

The meta-analysis compared the two in several ways¹:

• On free-weight tests, strength rose significantly more after free-weight training¹.
• On machine tests, strength tended to rise more after machine training, but the difference was not statistically significant¹.
• Each tested on its own equipment (the direct comparison), the groups showed no overall difference in strength, jump or muscle growth¹. Within it, upper-body strength rose more with machines, with no difference in the lower body¹.

It concluded that strength gains are specific to the equipment trained with¹. Whether people were trained or untrained did not change the results¹. An earlier 2022 meta-analysis found the same equipment match, and similar gains on a neutral testing device¹⁴. It found no difference in power or muscle size¹⁴.

Two single trials compared the two directly^3,15:

• 46 young adults, 8 weeks. The biceps and quadriceps (the four front-thigh muscles that straighten the knee) grew thicker, with no difference between groups³. Machine bench press strength rose more in the machine group, 13.9% against 8.6%³.
• 36 novice men, 10 weeks. Groups on machines only, free weights only, or machines then free weights made similar gains in strength and limb and chest size¹⁵.

Weightlifting-style training and jumping

Three meta-analyses compared weightlifting training with other training^5,16,17:

• 2016, six studies of 232 athletes and students with lifting experience. Vertical jump rose 5.1% more than with traditional resistance training, and did not differ from plyometric training¹⁶.
• 2018, seven studies. Gains in countermovement jump (a jump that starts with a quick dip) were 7.5%, against 2.1% with traditional training¹⁷. They did not differ significantly from plyometric training¹⁷.
• 2022, 16 studies of 427 people. Gains in weightlifting load and countermovement jump were greater than with traditional training, though results varied widely and risk of bias was possible⁵.

The 2022 analysis found no significant differences from plyometric training in speed, power or strength⁵. A 2015 review reports earlier studies suggesting pulling variations may train as well as, or better than, lifts with the catch⁶.

What studies found about injury

In the introduction to the 2023 meta-analysis, its authors judged it uncertain whether free weights and machines differ in injury risk¹. They noted that a higher injury rate reported with free weights mostly involved weights falling on people¹. They added that the evidence is mainly cross-sectional, looking at a group once¹. They report that the American College of Sports Medicine has argued machines may be safer, as they need less skill¹.

A US study estimated 970,801 weight-training injuries seen in emergency departments from 1990 to 2007¹⁸. Of these, 90.4% involved free weights, and the most common cause was a weight dropping on the person¹⁸. In 4,111 US emergency patients aged 8 to 30, the authors concluded most youth injuries were accidents, such as dropped weights¹⁹. A 2022 review of young weightlifters reports that injury rates appear relatively low and severe injury is uncommon²⁰.

Rates in the strength sports come from reviews that pooled mostly low-quality or looking-back studies^21,22:

Sport	Injuries per 1000 hours of training
Bodybuilding	0.24 to 122
Powerlifting	1.0 to 4.421
Weightlifting	2.4 to 3.321
Strongman	4.5 to 6.122
Highland Games	7.522

One review found these sports seem to have fairly low injury rates next to common team sports, though only four of its studies were prospective²². Another judged the risk in weightlifting and powerlifting similar to other non-contact strength and power sports²¹. Across resistance training, one review found rates from 0.21 to 18.9 per 1000 hours²³. It put much of the spread down to differing definitions of injury²³. It concluded traditional strength training had the fewest injuries of the methods compared, while noting few studies were rated highly²³.

In these sports, the sites most often injured were generally the lower back, shoulder, knee, wrist or hand, and elbow²². Strains (overstretched or torn muscles), tendinitis and sprains (stretched or torn ligaments) were the most common types²². Tendinitis is pain and swelling of a tendon, a tough cord of tissue that connects a muscle to a bone. A 2024 review found pelvic floor problems, such as leaking urine, in 50% of female and 9.3% of male weightlifters and powerlifters⁴. The pelvic floor is the sheet of muscle that closes the bottom of the pelvis.

Connections

The tissues and methods it relates to

The wider picture is on the resistance training page. In trials of healthy adults, resistance training raised strength more than no exercise did¹³. They load muscle: both kinds raised muscle size in the 2023 meta-analysis¹.

The back squat loads tendon, such as the patellar tendon (the band from the kneecap down to the shinbone)²⁴. In 10 strength-trained athletes, its strain rose as back squat load rose²⁴. Weightlifting training has been compared with plyometric training, with no significant differences found in speed, power or strength⁵.

Exercise pages that use them

• The back squat, bench press and deadlift, the three powerlifting lifts⁴.
• The overhead press, studied with a barbell and a machine¹¹.
• The barbell row, studied as a free-weight and a machine row¹⁰.
• The shrug, one of five dumbbell exercises in a trial of 447 office workers²⁵.
• The biceps curl, studied with a barbell and on a cable²⁶.
• The triceps extension, studied with dumbbells overhead and lying down²⁷.
• The wrist curl, part of a dumbbell programme in a study of 11 men aged 70 to 80²⁸.
• The single-leg Romanian deadlift, studied with dumbbells²⁹.
• The farmer’s carry, studied with two dumbbells³⁰.

Sources

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12. de Almeida Paz I, Frigotto MF, Cardoso CA, Rabello R, Rodrigues R (2022). Hip abduction machine is better than free weights to target the gluteus medius while minimizing tensor fascia latae activation.. Journal of Bodywork and Movement Therapies. doi:10.1016/j.jbmt.2022.01.001 PMID 35500965
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Every source the library cites

Changes

• September 30, 2026 First published.