The single-arm row, often performed with a dumbbell, is a foundational resistance exercise to enhance back strength and muscular size. This horizontal pulling movement requires the working arm to move a load from a lengthened position toward the torso. Unlike two-handed variations, the single-arm nature forces each side of the body to work independently. Understanding which muscles initiate and support this action helps maximize the benefits of this exercise.
Primary Muscles for Back Thickness and Width
The primary muscle for developing back width is the Latissimus Dorsi (Lats), the largest muscles of the upper body. During the pull, the Lats are the main drivers of shoulder extension and adduction, pulling the elbow toward the hip. They are responsible for the feeling of “flaring” the back that contributes to a wider physique.
The middle Trapezius and the Rhomboids are the major contributors to back thickness, located between the shoulder blades. These muscles execute scapular retraction, pulling the shoulder blade toward the spine. Engaging them fully requires a conscious effort to squeeze the shoulder blade inward at the top of the pull. The controlled lowering of the weight (eccentric phase) is important, allowing these muscles to be stretched under tension, which stimulates muscle growth.
Stabilizing Muscles and Core Engagement
While the Lats and Rhomboids initiate the movement, several smaller muscles act as synergists, assisting the primary pull. The Biceps Brachii flexes the elbow joint, which is an integral part of the rowing motion. The Posterior Deltoid, the rear head of the shoulder muscle, also assists in extending the arm back, particularly when the elbow is pulled higher and wider.
The forearm flexors and grip muscles are heavily activated, especially under heavy loads. The core musculature, including the Abdominals, Obliques, and Erector Spinae, plays a significant role in stabilization. Because the weight is only on one side, the core must forcefully resist rotational forces to keep the spine neutral and prevent the torso from twisting toward the working arm.
Shifting Focus Through Form Adjustments
Minor adjustments to the pulling angle can significantly alter the emphasis on the primary back muscles.
Maximizing Lat Activation
To maximize Latissimus Dorsi activation for back width, pull the elbow tightly toward the hip. This technique minimizes the range of motion for the upper back retractors and focuses the load on the larger, lower back muscle fibers. The torso remains relatively parallel to the floor, and the elbow stays close to the side of the body.
Emphasizing Upper Back Thickness
Conversely, emphasizing the upper back, including the Rhomboids and middle Trapezius, involves changing the elbow path. Pulling the elbow higher and wider encourages greater scapular retraction and upward rotation. This angle recruits more of the upper back muscles, along with the Posterior Deltoids, contributing to thickness and improved posture. This variation is often referred to as a “high row.”
Why Unilateral Training Matters
The single-arm nature of this exercise offers distinct advantages over two-arm variations. Training one side at a time allows the lifter to address and correct existing muscle imbalances between the left and right sides of the body. When using two arms, the stronger side often compensates for the weaker side, worsening strength disparities.
The single-arm row uniquely increases the demand on the core’s anti-rotation and anti-lateral flexion capabilities. The core must actively brace to maintain a straight, stable torso against the uneven load. This increased stabilization translates into improved functional strength and better control of the trunk, which benefits movement efficiency and injury prevention.