Throughout the past year and a half, having the ability to effectively train outside the gym has become more valuable than ever before in recent history. While COVID-related gym closures have now mostly ended throughout the globe, not all lifters have returned to training in gyms. Many lifters have opted to continue training at home where equipment is often limited but the monetary and time costs are lower than renewing gym memberships and regularly commuting. Survey data from over 11,000 participants who were previously attending gyms found that approximately 35% of Americans and 28% of people globally did not intend to return to training at gyms (24). For those who have returned (or intend to in the future), knowing how to train effectively with minimal equipment can still be immensely beneficial when traveling, and minimal equipment does not have to translate to minimal results. For the majority of people, most muscle groups can be successfully stimulated to strengthen and grow from training at home with a couple resistance bands, a pullup bar, and proper exercise selection. However, some muscle groups such as the quads may pose more of a challenge to effectively train at a home that lacks a barbell, power rack, and weight plates. Performing a typical quad workout consisting of some combination of barbell squats, leg presses, hack squats, and machine leg extensions may simply not be possible.
If you have sufficiently heavy dumbbells, rear foot elevated split squats are a viable means of building the quads at home. However, many people lack dumbbells heavy enough to reasonably load this exercise if they are stronger than the novice level, and heavy dumbbells can be a pricey purchase. One way to expose the quads to a higher magnitude of tension without heavy weights is to perform a truly unilateral exercise such as a pistol squat where the entirety of loading is transmitted into one leg rather than having the rear leg provide assistance with a split squat or lunge. However, the vast majority of individuals lack the mobility required to properly execute a pistol squat. Skater squats are a viable alternative that do not necessitate the same degree of mobility as pistol squats do, and they may challenge the quads when performed with a pair of relatively light dumbbells. Unfortunately, balance rather than quad strength may be the limiting factor for some people when performing skater squats, providing a poor stimulus for hypertrophy. Additionally, complete quad development cannot be achieved from exclusively using compound exercises due to the anatomy of this muscle group.
Dumbbell Skater Squats
Multi-joint exercises where knee extension is performed simultaneously with hip extension, such as squat and lunge variations, effectively train the vastus lateralis, vastus medialis, and vastus intermedius. These three monoarticular (i.e. crossing only one joint) muscles originate from the femur and exclusively function as knee extensors (25). In contrast, the other muscle of the quadriceps, the biarticular (i.e. crossing two joints) rectus femoris, originates from the pelvis and functions as both a knee extensor and hip flexor (25).
Notably, the rectus femoris does not just weakly assist in flexing the hip, but rather functions as a primary hip flexor that has greater leverage for producing hip flexion torque than any other muscle in the human body at certain joint angles (21). Because contraction of the rectus femoris can produce a substantial amount of hip flexion torque, its recruitment during a movement that requires both hip and knee extension is less biomechanically efficient than recruitment of the other muscle bellies of the quadriceps. As the rectus femoris contracts more forcefully during a movement like the squat, the hip extensors must work harder to resist the hip flexion torque it produces. Striving to maximize efficiency, the nervous system preferentially recruits the three monoarticular muscle bellies of the quads to a greater degree than the rectus femoris during compound exercises where extension simultaneously occurs at the hip and knee joints (4, 7, 8, 10, 12, 22). For this reason, squats, leg presses, and lunges can effectively increase the size of the vastus lateralis, vastus medialis, and vastus intermedius, but fail to induce any significant hypertrophy of the rectus femoris (6, 16). However, during a single joint knee extension exercise where no movement occurs at the hip joint, the rectus femoris is just as active as the monoarticular muscles of the quad, if not more so (11, 20, 23, 27). Consequently, machine seated leg extensions have been demonstrated to produce a considerable degree of hypertrophy of the rectus femoris that is similar to or even more pronounced than that of the three vastii muscles (9, 14, 18, 20, 26, 27).
While you may not have a leg extension machine at home, the reverse Nordic curl serves the same function without requiring any equipment. To perform the reverse Nordic curl, kneel on a padded surface such as a Pilates mat or foam pillow to provide cushioning for your knees. Begin the movement by tensing your abs and glutes to brace your core while your torso is in a vertical position. While keeping your hips extended and torso rigid, gradually lean backwards by flexing at the knees. Descend as far as you can control the movement and then return to the starting position by extending your knees.
During this exercise, the training stimulus presented to the quads is provided by resistive torque acting on the knee joints. Torque is the product of a force (i.e. the product of mass multiplied by acceleration) multiplied by its moment arm length (i.e. the perpendicular distance between the line of force and the axis of rotation). During a reverse Nordic curl, the knee joint is the axis of rotation, and the resistive force is the product of gravitational acceleration multiplied by body mass located above the knee joint. The moment arm, also known as the lever arm, is the perpendicular distance between the knee joint and the body’s center of mass. When standing, the body’s center of mass is typically located near the navel. When kneeling during the reverse Nordic curl, the center of mass will lie higher up in the abdominal region. As the angle of knee flexion increases during the descent, your center of mass moves a greater perpendicular distance from your knee joint. Consequently, the magnitude of resistive torque increases, requiring your quads to produce greater knee extension torque in turn.
The following two images depict the aforementioned biomechanics of the reverse Nordic curl. The red circle represents an approximation of the body’s center of mass. The green circle represents the knee joint’s axis of rotation. The yellow line represents the line of gravitational force directed downward from the center of mass. The purple line represents the moment arm length of the resistive torque acting on the knee joint.
The increase in resistive torque throughout the eccentric phase results in the reverse Nordic curl having an ascending exercise strength curve. With this strength curve, the end range of motion (ROM), corresponding to the start of the concentric phase and peak angle of knee flexion, is the most challenging portion of the movement.
As a result, the exercise can be tailored to an individual’s strength by being performed with a partial ROM by less experienced lifters or with a full ROM where the upper back contacts the ground by more advanced lifters. Rather than increasing the load, intensity progression can occur by increasing the ROM until a full ROM is achieved. Alternatively, the angle of hip flexion may be manipulated to vary intensity. As the angle of hip flexion increases, the body’s center of mass will shift forward toward the knee joint, resulting in lower knee extension torque demands during the exercise. If an individual lacks the strength required to perform the reverse Nordic curl through a full ROM with an extended hip position, full ROM reps may still be performed by utilizing a more flexed hip position. Similar to progression via increasing ROM, reverse Nordic curl intensity may be increased by decreasing the angle of hip flexion maintained throughout the exercise until a neutral hip position is achieved.
If you can perform the reverse Nordic curl with an extended hip position through a full ROM for a moderately high number of reps, you can increase the intensity by raising your arms above your head, which shifts your body’s center of mass further away from your knee joint. Alternatively, you can hold a weight plate or dumbbell to your chest, but this additional load will not be required for the vast majority of people who ever attempt to perform this exercise through a full ROM with arms held overhead. Mechanical drop sets can also be readily performed with this exercise. After fatigue accumulates during a set and you can no longer perform full ROM reps, you can perform reps with a progressively shorter ROM or more flexed hip position if you wish to train your quads until failure.
Beyond its convenience, the reverse Nordic curl also provides some advantages over machine seated leg extensions. With the extended hip position involved with a reverse Nordic curl, the gluteus maximus is trained isometrically (since you are tensing your glutes to lock your pelvis in place) in a manner similar to holding the position of peak contraction during a glute bridge. Furthermore, during this exercise, the rectus femoris can be trained at longer muscle lengths than with a seated leg extension. Because the rectus femoris functions as a hip flexor, it is shortened at the hip joint in a seated position and therefore operates at short to moderate muscle lengths during a seated leg extension. During the end ROM of a seated leg extension’s concentric phase, the rectus femoris is shortened at both the hip and knee joints.
When a biarticular muscle is simultaneously shortened at two joints, it may experience active insufficiency, a phenomenon which limits how much force can be produced by the shortened muscle. Force is generated within the functional units of muscle, known as sarcomeres, when the contractile proteins actin and myosin are able to bind together to form crossbridges (13). At very short sarcomere lengths, little overlap between actin and myosin is present, and relatively few crossbridges can be formed, resulting in low force production capacity (5). This decreased force production at short lengths can readily be observed if you make a firm fist and then fully flex your wrist while attempting to maintain the tight fist. Because of active insufficiency, you can flex your fingers more forcibly with a neutral wrist position compared to a flexed wrist position. In addition to functioning as wrist flexors, the flexor pollicis longus can flex the thumb, and the flexor digitorum superficialis can flex the other four fingers. When the wrist is in a neutral position, actin-myosin overlap within the constituent sarcomeres of these two muscles is high enough to form a large number of crossbridges during finger flexion, therefore facilitating high force production. When the wrist and fingers are simultaneously flexed, the sarcomeres of these muscles are shortened to the extent that relatively little actin-myosin overlap is present. In this state of active insufficiency, fewer crossbridges can be formed within the sarcomeres of the flexor pollicis longus and flexor digitorum superficialis, resulting in diminished force production capacity.
Because muscle fibers experiencing a high magnitude of tension is a primary determinant of hypertrophy, training a biarticular muscle as it is simultaneously shortened at two joints is suboptimal for inducing hypertrophy. In contrast to seated leg extensions, when knee extension is performed with an extended hip position during reverse Nordic curls, the rectus femoris can be loaded at long muscle lengths, where active insufficiency does not occur but stretch-mediated hypertrophy may be induced. This may result in a greater magnitude of rectus femoris growth than could otherwise be achieved from training at shorter muscle lengths with seated leg extensions (17,19). Indeed, research has found seated leg curls, which train the biarticular hamstrings at long muscle lengths, to yield greater hypertrophy than lying leg curls, which train the biarticular hamstrings at short muscle lengths (17). For a deeper dive into the details of this hamstring training study conducted by Maeo et al., check out the analysis (subscription required to access) written by Greg Nuckols in Volume 4, Issue 12 of the MASS Research Review.
For individuals without experience performing reverse Nordic curls, the volume and intensity of this exercise can be gradually progressed as they build up more strength and proficiency with the exercise. Alonso-Fernandez et al. conducted an 8-week reverse Nordic curl intervention with 26 recreationally active subjects and found that performing 2-3 sets 2-3 times per week was sufficient to induce significant increases in rectus femoris thickness and cross-sectional area (1). More experienced individuals will likely require a greater stimulus for further hypertrophy, but initially employing a conservative progression may be prudent because both the quads and knee joint experience a high magnitude of loading during this exercise. In response to training, neuromuscular function may improve more rapidly than adaptations occur to connective tissues such as tendons (15). Correspondingly, a sudden spike in reverse Nordic curl volume and intensity may result in knee extensor strength increasing at a faster rate than the load tolerance of the knee joint’s connective tissue. An athlete’s risk of injury has been found to be elevated when his acute workload meaningfully exceeds the chronic workload to which his body has been accustomed, so a gradual progression of the training stimulus is warranted (2, 3). Additionally, not every exercise is right for every person even when a conservative progression is utilized. For instance, deficit deadlifts and full ROM weighted dips are quality exercises, but they may be inappropriate selections for some individuals due to previous injury or mobility restrictions. Just as lying tricep extensions may be suboptimal for some lifters with prior elbow joint issues, so too may reverse Nordic curls not be suitable for some people with prior knee injuries.
In conclusion, whether your goals are to enhance the strength or aesthetics of your quads, reverse Nordic curls are a valuable exercise, especially when training at home.
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