INTRODUCTION
The reemergence of the kettlebell (KB) has spawned a host of training routines using this resistance-training tool. A search on YouTube using the term “kettlebell training” returns more than 100,000 related videos. In contrast, a search of the National Library of Medicine (PubMed) using the same search terms results in only 10 peer-reviewed citations. The large volume of online video instruction indicates the popularity of the KB, but the majority is produced by amateurs, and may include unsafe techniques that could lead to injury.
Thus, there is a need for an evidence-based approach to the benefits and use of this training tool. Although the design of the KB is very simple, the exercises executed with a KB are not simple movements and need to be approached with the goal of learning to complete each movement with proper technique to reduce the risk of injury (7,9). The aim of this article was to highlight the benefits of KB training as supported by scholarly research, the importance of using proper technique, and to offer basic recommendations for the management of risk when training with KBs.
BENEFITS OF KETTLEBELL TRAINING
The American College of Sports Medicine's guidelines classify an activity that produces at least 76% of maximum heart rate (HRmax) as “vigorous” exercise capable of improving cardiovascular fitness (1). Farrar et al. (2) reported an average of 86% of HRmax in college-aged, recreationally trained, male subjects performing the 2-handed swing exercise with a 16-kg KB for 12 minutes and resting only “as needed” while trying to complete as many KB swings as possible.
Hulsey et al. (4) indicated that KB training imposes enough of a challenge to the cardiovascular system to meet the criteria for improving aerobic fitness. The authors in this study had the college-aged participants employ a work-to-rest ratio of 35 seconds of work to 25 seconds of rest with participants using either an 8-kg KB (female) or a 16-kg KB (males) for 10 minutes. In contrast, Jay et al. (6) found no significant improvement in aerobic capacity in their participants (mean age: 44, ±8 years), which were prescribed KB swing training 3 times per week for 8 weeks. The intervention consisted of 10–15 minutes of interval training with an external resistance that could begin at 0 (unweighted swings) or an 8-kg KBs for female participants and a 12-kg KBs for male participants. In addition, the work-to-rest ratio during the first 4 weeks of this study consisted of 30 seconds of KB movement followed by 1 minute of active rest consisting of walking and “shaking arms and legs.”
The discrepancy between the published results of Farrar et al. and Hulsey et al., which indicate the potential for improved cardiovascular fitness with KB training, and that of Jay et al, may be due to a dose-response issue. The authors explained as much in their discussion of the study results where they attributed the lack of an aerobic improvement to “insufficient cardiovascular stimulation.” Data supporting the use of high-intensity interval training (15) suggest that a more robust training stimulus using the KB may improve aerobic fitness.
The evidence supporting the use of KB training to improve strength and power, like the studies investigating the cardiovascular benefits of KB training, is inconsistent. The inconsistent research results with regard to KB training for improvements in strength and power are a little surprising when the principle of specificity is applied to this method of training. KB training, which requires the practitioner to quickly accelerate and decelerate a moving external load, should result in more powerful muscular contractions. For those studies that have progressed their participants through more challenging bouts that overload the musculoskeletal and neuromuscular systems, increases in strength and power have been the result. Three studies (7,9,14) cited improvements in power and strength.
A study by Lake and Lauder (7) employed biweekly exercise bouts for 6 weeks for both a treatment group (KB) and a control group (jump squat). The KB group's treatment was composed of 12 rounds of 30-second work to 30-second rest bouts of KB swings (3 sets of 6 repetitions), accelerated KB swings (4 sets of 6 repetitions), and goblet squats (4 sets of 6 repetitions) using a 16-kg KB. The control group for this study performed at least 3 sets of 3 jump squats with the barbell load adjusted to achieve peak power. The investigators then compared pre- and postintervention data on the dependent variables of strength using a half squat 1 repetition maximum (1RM) and vertical jump height for explosive power.
In a study by Manocchia et al. (9), the effects of a 10-weeks KB intervention on strength, power, and endurance was investigated in physically active men and women. In this study, the treatment group participated in biweekly bouts of various KB exercises (e.g., push-presses, squats) that varied volume, pace, and intensity with the goal of emphasizing strength, power, or muscular endurance. This study was unique in its use of a periodized delivery of the KB intervention that progressively increased training intensity. For example, the first microcycle had the treatment group working through a series of 2 sets per KB exercises for 15–20 repetitions at 60–65% of a 0–10 RPE scale. By the fifth microcycle, the participants were performing more complex movements (e.g., Turkish getup) for 2–3 sets of 4–8 repetitions at 80–85% of the RPE scale. Manocchia et al. reported significant increases in strength (3RM bench press) and power (3RM clean and jerk).
Among the few published KB studies, 2 have found no improvement in lower body power as measured by jump height (6,9) and another (8) suggested that KB training might not impose sufficient stimulus to the musculoskeletal system to result in improved muscular strength. It should be noted that the article by Lake and Lauder (8) was a kinetic study comparing the KB swing, the back squat, and the jump squat with no training intervention employed, unlike the studies previously summarized that delivered an intervention and did present data for improvements in muscular strength. The intervention of Jay et al. (9) reported no improvement in muscular power as measured by countermovement jump height after 8 weeks of KB training 3 times per week. As with the earlier study by Jay et al. (6), this investigation employed shorter working bouts (30 seconds) followed by longer resting intervals (30–60 seconds) and used lighter KBs (8-kg for female and 12-kg for males) when compared with the studies just summarized. Although the evidence supporting KB training to improve muscular strength and power is not unequivocal, studies that prescribed larger exercise volumes, shorter rest periods, and heavier loads, reported significant improvements in strength and power.
In terms of reducing lower back pain, the investigations into the potential benefits of KB training are encouraging. It may be that the eccentric loading of the hamstrings that occurs with KB swings could be protective for athletes (10) who experience eccentric loads during sport (e.g., swing phase during sprinting). A study by Jay et al. reported reductions in lower back pain after 8 weeks of KB training (5). These results have additional support in a different study by Jay et al. (6) who found that their 8-week KB training protocol resulted in improved stability of the back extensors in response to a postural challenge. One reason for the ability of KB training to improve back health may come from enhanced activation of the back and hip extensors. Jay et al. (6) uses the term “Sensory motor amnesia” and McGill (11), “gluteal amnesia,” both in reference to a lack of sensory motor control of the back and hip extensors and its connection to back pain and injury. Because KB training, done correctly, requires the generation of muscular power from the hip extensors with a stiffened core and neutral spine, it seems to be ideally suited to helping people produce power from their hips while controlling unwanted movement of their trunk.
POTENTIAL RISKS WITH KETTLEBELL TRAINING
A word of caution is warranted regarding KB training. Training with KBs, like any other exercise that involves accelerating and decelerating an external load, brings with it inherent risks. Research by McGill (11,12) implies that intervertebral discs are at increased risk of injury with lumbar flexion motion and that this risk is increased as load to the discs increases significantly during loaded lumbar flexion. It is also important to note that McGill measured shear forces (posterior force on L4 relative to L5) during the KB swing that is different from conventional bar lifting. The ratio of shear to compression forces in the top half of the swing may irritate the spine of individuals who have unstable lumbar joints and may increase the amount of compressive load on the spine (13).
Although many people with back pain do well with KB swings, McGill recommends a shear test to help predict those who will experience a flare-up of symptoms. In terms of managing injury risk while training with the KB, it is important that the KB practitioner be coached to maintain the neutral lumbar curve while working with the KB. McGill (13) has also shown that conscious bracing of the abdominal wall during the swing will further stabilize the spine adding training tolerance to the exercise. This is likely what motivated a few of the investigators (4,7,9) to use “certified” and “trained professionals” to supervise their experimental subjects. It is imperative that fitness professionals who prescribe KB training for their athletes/clients seek out expert training for themselves and insist on safe and effective technique and progression in their clients at all times.
RECOMMENDATIONS FOR SAFETY AND EFFECTIVENESS DURING KETTLEBELL TRAINING
Novice users of KB exercises should be coached by a fitness professional with experience in KB training. Professional KB certification can be 1 indicator to the athlete/client that the instructor has the recommended instruction and experience in KB training.
One of the failings of many instructional sources available for KB training is that they demonstrate KB movements with a nonneutral spine (e.g., flexed or hyperextended cervical, thoracic, or lumbar spine). Flexion of the lumbar spine during movement increases the risk of injury to the lower back (12). The primary function of the muscles that control movement in the lumbar spine (i.e., the “core”) is to stiffen and brace the lumbar vertebrae in their neutral position as forces are transmitted from the lower body up through the kinetic chain (12). This means that the coach must be able to demonstrate and insist on the maintenance of the natural curvatures of the spine during KB exercises (Figure 1).
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Figure 1: Bottom position of the 2-handed KB swing with maintenance of a neutral spine (i.e., neutral kyphotic and lordotic curves).
Given that one of the proposed benefits of KB training is to help reestablish sensory motor control of the back and hip extensors (6,13), it is important that these muscle groups be the focus of attention when coaching KB movements. During an exercise like the KB swing, the instructor must be able to coach the proper stiffening of the core and the generation of power from the hips. A variant of the KB swing often demonstrated has the participant squatting the KB (Figure 2).
Figure 2: A KB swing variant often demonstrated with the practitioner squatting the KB during the swing.
A squat results in a more vertical path at the shoulders and hips while the movement of the KB follows a curved path. The result is that the muscular force generated during the concentric phase of a squat produces a vertical force that results in a lack of force transmitted to the curvilinear path of the KB. The result will be that the practitioner will need to generate force at the shoulders to move the KB up to the demonstrated shoulder height. If the training goal was to improve core strength and power generation at the hips, the client should not have to use their arms to move the KB. The arms are merely chains connecting the KB to the motive power generated by the hips. To overcome a KB's inertia and give it momentum requires powerful contractions of the hip extensors with the resultant forces transmitted to the upper body through a stiffened core (see Video, Supplemental Digital Content 2, https://links.lww.com/SCJ/A132, demonstration of proper hip extension with maintenance of a neutral spine during a 2-handed KB swing).
The prescribed load must match the objectives of the program, the lifter's skill level, and fatigue level. KBs are normally produced in 4-kg increments (e.g., 4 kg, 8 kg, 12 kg). In the peer-reviewed articles cited in this article, investigators most often used a beginning load of 8 kg for women and 16 kg for men. When deciding on a KB load, the coach's aim should be to ensure that a) the load is safe (i.e., the practitioner can maintain good form) and b) the load is effective (i.e., the principle of overload is being applied).
When having an athlete/client perform an extended set or multiple sets, fatigue will have an effect on safety. The coach/trainer should adjust the load if proper form cannot be maintained throughout the set.
A PERIODIZED APPROACH TO KETTLEBELL TRAINING FOR STRENGTH, POWER, AND ENDURANCE
To date, there has been very little attention given to program design and movement-specific technique (3,10). This section aims to address this by illustrating the fundamental technique for the clean and jerk and the snatch and by offering a sample periodized KB program aimed at improving muscular strength, power, and endurance.
The 2 fundamental movements presented here are the clean and jerk and the snatch. These movements are particularly beneficial to the development of strength, endurance, and power for 4 specific reasons. Both are full body movements. They both rely heavily on hip activation, the part of the body with the largest contribution to lower body power. Both movements engage the muscles that maintain spinal stability. Finally, when KB training is programmed for pace, both movements result in an elevated cardiovascular demand.
THE CLEAN AND JERK
The clean and jerk is a 2-stage movement. Begin with the KB on the ground. Grip the KB loosely in cradle of the fingers with the thumb rotated back to point in the direction of the opposite foot (Figure 3).
Figure 3: Hook grip for use with any swing, clean, or snatch.
The thumb should be hooked over the handle of the bell and lying over nail of the middle or index finger. This is called the hook grip.
The bell should be placed slightly forward of the lifter's body. When lifting the bell from the ground, this position will allow gravity to start the bell's movement to a position behind the lifter's knees (i.e., the backswing) (Figure 4).
Figure 4: Starting stance allows gravity to begin the swing when the KB is initially lifted.
At the apex of the backswing, the lifter should powerfully extend the hips. The forceful hip extension will move the arm back out in front of the body. When the KB reaches chest height, he/she should sharply retract the shoulder girdle to change the vector of the bell back in the direction of the lifter's body. This action will initiate the rotation of the KB. It is during the scapular retraction phase that the lifter should allow the handle to shift from the cradle of the fingers (i.e., hook grip) and into the palm of the hand. This is done to reduce friction across the finger joints. Avoiding bell rotation while the handle is in contact with these joints prevents blistering and skin tearing. A correct catch position places the bell handle diagonally through the palm running from the first joint of the index finger to the heel of the palm. The bell should simultaneously contact the forearm, upper arm, and chest as it settles into rack position (Figure 5).
Figure 5: In the rack position, bell should rest against the chest, upper arm, and forearm. The hand should be relaxed.
To initiate the jerk, the lifter must have a solid base of support at the 3 points of contact in the rack position. This allows for maximal transfer of power from the body into the KB. From the rack position, the lifter then sinks into slight flexion at the hips and the knees followed by quick extension. The power-focused lower body contraction transmits force from the lower body, through a stiffened core, up through the torso and to the racked KB. If the extension phase of the jerk is performed correctly, the KB should not leave the body until full extension is achieved at both hip and knee. If the coach/trainer notes that the KB is leaving the rack position before full hip and knee extension, this indicates that the lifter is pressing the bell using the arm instead of transmitting force to the KB from the lower body. As the bell ascends, the hips and knees relax back into a position of slight flexion at the hips and knees until the elbow locks. At this point, the athlete should again extend the hips and knees to achieve overhead lockout (Figure 6A–D).
Figure 6: (A–D) The jerk consists of 4 distinct parts: The initial dip, extension, undersquat, and lockout.
After safe fixation of the bell overhead, allow the bell to return to the rack position. The lifter immediately rolls the KB out of rack position and into the next backswing. As the bell exits the rack position, the lifter should elevate the shoulder of the lifting arm and lean back behind his/her center of gravity to prepare the back and hips for the eccentric phase of the swing. This movement also helps to ensure that the KB falls along a curvilinear path rather than falling straight down which helps to absorb shock (Figure 7).
Figure 7: Just before the bell drops out of rack, the lifter should shift their body back behind their center of gravity to allow for efficient counterbalance and shock absorption.
As the KB passes the waist, allow the lifting shoulder to follow the KB and rotate toward the ground into the backswing (Figure 8).
Figure 8: Body position at the end of the eccentric phase of the clean and jerk. This position sets the lifter up for an efficient power transfer and shoulder retraction in the next clean.
THE SNATCH
The snatch begins in a similar way to the clean. The snatch, however, requires greater hip activation as the goal is to lift the KB above the lifter's head in 1 movement. Given this fact, it will be necessary to begin training this movement with a lighter KB than was used for the clean and jerk. Start with the same grip and body position as illustrated for the clean and jerk (see Figures 3 and 4). The power phase of the snatch begins like the clean and jerk with the difference appearing as the shoulder retracts. As the KB reaches the bottom of the chest, the lifter retracts the shoulder and allows the elbow of the lifting arm to flex passively. The hand should slightly supinate as the bell ascends. When it reaches approximately chin height, the lifter should quickly reverse shoulder retraction into protraction and forcefully push his/her hand into the bell handle. The bell should drift into an overhead lockout position as the elbow straightens with the KB handle lying diagonally across the palm as in the clean (Figure 9A–C).
Figure 9: (A–B) As the bell ascends in the snatch, retraction followed by protraction at the shoulder girdle allows the hand to insert into the bell handle for a smooth low-impact catch.
With the completion of a solid catch, the lifter initiates the eccentric phase of the snatch by externally rotating the shoulder and flexing the elbow to begin the descent of the KB. As with the clean and jerk, as the KB reaches the shoulders, the lifter will shift his/her center of gravity back to make the KB swing rather than drop and will internally rotate at the shoulder and wrist in preparation for the backswing (Figure 10A–D).
Figure 10: (A–D) Internal rotation of the shoulder with elbow flexion initiate the eccentric phase of the snatch followed by internal rotation in preparation for the backswing.
For reasons of both safety and comfort, when performing either the clean and jerk or the snatch, it is important to make them as smooth and fluid as possible. Jerky movements and heavy bell impacts on the body will result in acute and chronic injuries and discourage the lifter from using this training tool.
A PERIODIZED KETTLEBELL PROGRAM
When programming KB movements, it is beneficial for the coach/trainer to treat them similarly to program design for Olympic-style lifts. With competent coaching, a working understanding of the movements may be achieved in a relatively short amount of time. However, due to the complex nature of the movements, they may take years to master. Overuse injuries tend to be most common in KB lifters with relatively little experience. Issues such as bell impact on the wrist, improper jerks leading to shoulder injuries and poor rack positions can lead to back pain or injury. To gain the maximal benefit from KB training, it is critical to develop a high level of competency by focusing on KB-specific programming as opposed to immediate integration of KBs into a general strength and conditioning program.
To maximize the potential for gains in strength, endurance, and power, KB sets should initially be set up to focus on 3 central components:
- a. Endurance intensive sets: typically characterized by longer near maximal endurance sets with lighter loads.
- b. Strength intensive sets: typically characterized by shorter near maximally loaded sets with shorter duration and lower numbers of repetitions.
- c. Pace/power-focused sets: typically characterized by sets that are more moderate across all loads and repetitions that emphasize a constant output of work over time, thus power.
This approach will have the athlete working across a spectrum from heavier loads with short repetition schemes to the lighter loads with extended repetitions that impose a significant cardiovascular demand. When integrated into a periodized program, the athlete will develop increased endurance, baseline strength, and a capacity for power production over time.
When setting up and progressing the athlete through this program, traditional programming guidelines should be followed.
- a. Only 1 variable should be adjusted at any given time.
- b. Begin the design of the macrocycle by establishing the cycle's primary training goal.
- c. Create a corresponding mesocycle structured to support the goal of the macrocycle.
Following these guidelines will guide the coach in determining how heavily each mesocycle is weighted toward either endurance, strength, or pace/power sets.
Whereas each macrocycle will be weighted toward eliciting 1 primary training effect, every mesocycle will contain all 3 types of sets (e.g., endurance, strength, and pace/power). The bias of that particular mesocycle will determine how many endurance, strength, and pace/power sets are programmed. Similarly, each training day should have some small element of each type of set with a bias for that day's central theme (i.e., a microcycle). For example, on an endurance-focused day, the athlete may be lifting 16-kg, 20-kg, and 24-kg KBs. Most likely, the majority of the time in that particular microcycle will be spent with the 16-kg and 20-kg bells. If it were a strength-oriented day, the 24-kg bell would take more prominence.
Table 1 provides an example of an endurance-focused training day. On this day, the athlete will use a 20-kg KB to complete 20 repetitions in 2 minutes with 1 hand, immediately switch to the opposite hand, and complete another 20 repetitions in another 2 minutes. This first set will be followed by a 3-minute recovery. The athlete will then complete 8 repetitions in 1 minute with each hand using a 24-kg KB before taking a 2-minute rest. Finally, the athlete will complete 30 repetitions within 2 minutes and 30 seconds for each hand.
Table 1: Sample of an endurance-focused training day
Note that as this is an endurance-focused day, the larger portion of time is spent with the 16-kg KB to draw out the amount of time the athlete can spend under load without rest. Additionally, the rest interval leading into the 16-kg set is shorter as not to allow for full cardiovascular recovery from the preceding set.
Depending on the athlete, Table 2 illustrates what a progression of this endurance-focused program might look like.
Table 2: Sample progression of an endurance-focused program
In the above example, because endurance is the focus of the mesocycle, there is a need to increase the athlete's total time under load. When comparing Table 1 and Table 2, note that 30 seconds is taken from the 20-kg set and added to the 24-kg set to aid in increasing the athlete's familiarity with heavier loads. To compensate for a shorter first work set and to keep the heart rate elevated across the entire microcycle, 30 seconds was removed from the first rest interval as well. Because the demands of the second work set are increased, the 30 seconds taken from the first rest interval have been added to the second. Finally, an additional 30 seconds and 5 repetitions have been added to the last work set.
In contrast, if the emphasis were placed on strength during the microcycle, the bias would shift toward heavier KBs with greater rest intervals. If the periodized design leaned toward pace/power microcycles, the goal would be to train to improve the athlete's stamina under load. This would require moving the focus away from maximal strength or cardiovascular endurance and toward maintaining a steady effort over systematically increasing amounts of time. Thus, the bias would shift toward moderation of load and set length.
As in general program design, when setting up a macro/meso/micro structure, baseline strength takes the greatest relative time to develop. After baseline movement proficiency is established, early mesos should be strength biased. Pace would generally be the second goal with endurance third. Intermediate mesos will usually be structured around pace as the primary goal with strength secondary and endurance tertiary. Later stage mesocycles prioritize endurance, pace, and strength in that order.
A SAMPLE 90-DAY PERIODIZED PROGRAM
The following is one example of a periodized KB program. Table 3 shows the training focus of each mesocycle.
Table 3: Mesocycle
Table 4 organizes the microcycles based on a 5-day training week. The duration of each mesocycle is 4 weeks.
Table 4: A periodized KB program for improved strength, power/pace, and endurance
PRACTICAL APPLICATIONS
The KB has become a popular tool for the strength and conditioning professional interested in adding another approach to improving muscular strength, power, and endurance. Although a few of the studies(7,9,14) that employed higher loads and training volumes reported improvements in strength and power. Given the inconsistent findings among the small number of research studies done on KB training, more research is needed that investigates the efficacy of KB training to improve cardiovascular fitness, strength, power, and any protection that this type of training may offer in terms of reducing lower back pain.
Given the importance of proper instruction of KB exercise to reduce the risk of injury, coaches should weigh the proposed benefits of KB training against the risk of injury when proper form has not been learned and expert supervision is not consistently available. Given that a few researchers have measured increases in strength and power when employing higher loads and training volumes, the authors of this article offer a sample periodized training program with the goal of improving muscular strength, power, and endurance. The sample offered, while having anecdotal support for its efficacy, is not unequivocally supported by the research evidence. We would encourage investigators interested in KB training to test the merits of KB training using the scientific method. For those who are already using KBs in their training prescriptions, the priority of any new KB training regimen should be the safety of the lifter and the development of movement proficiency.
Beginning with 1 or 2 KB movements and a periodized program, as opposed to using KBs as part of a general conditioning program, supports the development of movement proficiency by allowing both coach and athlete to focus on a smaller set of training variables. From the point that both athlete and coach are comfortable with the athlete's performance with the KBs, it becomes much safer and beneficial to look for the strategic points within the general conditioning program that the KB may be best used. All health and fitness professionals who look to the KB can help their athletes, clients, and patients by contributing new research findings on KB training and insisting that high standards of athlete/client safety and coaching are maintained at all times.
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