This study aimed to gain an expert consensus on the best exercises for specific muscle groups to incorporate into PT programs aiming to enhance the five areas of functional strength in firefighter recruits. The top three exercises for each functional movement, as ranked by the expert group, were the following: for pushing, the top exercises were the push-up, sit-up, and jumping jack; for pulling, the top exercises were the push-up, jumping jack, and sit-up; for lifting, the top exercises were the jumping jack, push-up, and jumping squat; for carrying, the top exercises were the push-up, plank, and sit-up; and for dragging, the top exercises were the jumping jack, sit-up, and jumping squat. These exercises are functional, multi-joint exercises that target agonist and antagonist skeletal muscle groups and mimic movements of daily life for firefighters. The identification of these exercises facilitates PT planning, allowing common groupings of skeletal muscles to be targeted simultaneously to enhance core strength and cardiovascular adaptations. Each exercise was assigned modifications according to individuals’ ability by manipulating load by body weight and firefighting equipment or adjusting repetitions. Although the push-ups, sit-ups, and jumping jacks were frequently listed by the participants, this discussion highlighted only the push-ups and jumping jacks as a central pillar of discussion. These two calisthenic and vigorous-intensity exercises (defined as having an energy cost of 8 kcal/kg/hour) [9] are often used for disciplinary purposes during recruitment.
The push-ups was a frequently listed exercise for addressing the pushing, pulling, lifting, and carrying movements. It is a fast and effective exercise that directly targets the strength and endurance of the chest, shoulder, arm and core muscles and indirectly targets the quadriceps and hamstring muscles depending on the type of push-up performed and its variations [14], frequency and intensity. Hence, using this exercise, multiple areas of functional strength for firefighters can be repeatedly addressed over 8 weeks of training [15]. In this study, the experts suggested that the push-up exercise and its variations, using body weight for beginner and intermediate levels and firefighting equipment for advanced levels, were beneficial for improving upper body functional strength. The experts favoured standard push-ups over the knees-bent version because it looks more heroic and effective, which has been corroborated in a previous review [16]. A team of researchers demonstrated that standard push-ups and the knees-bent version elicited a ground reaction force of 64% and 49% of the exerciser’s body weight, respectively, while the exerciser is in the starting position [17]. Thus, the standard push-up is superior to the knees-bent version, and the weight supported by the arms is more than the load of 60% of the 1RM recommended for strength training. Often, the knees-bent version was chosen as a regression. However, both the standard push-ups and the knees-bent version have been shown to induce muscle hypertrophy and muscle gain when they are performed to failure [15] and produce similar isometric strength [16], findings that have been supported in recent research [4]. To improve local muscular endurance, the experts set 30, 50, and more than 50 repetitions as the volitional failure cut-off points for the beginner, intermediate, and advanced levels. These values correspond to the above-average (30–39 repetitions) to excellent (> 47 repetitions) push-up norms for men aged 20–29 years [18]. Interestingly, the chosen cut-off points may have multiple applications. The push-up has been identified as a protective health indicator for cardiovascular disease (CVD) events within 10 years. A group of researchers reported that across a sample of 1,562 active firefighters, those who completed more than 40 push-ups were 96% less likely to experience a CVD event compared to those who completed fewer than 10 push-ups (IRR, 0.04; 95% CI, 0.01–0.36) [19]. The researchers further revealed the number of push-up repetitions to be a better protective factor than a VO2max of greater than 42 mL/kg/min.
In this study, the experts identified the weighted standard push-ups as a progression for the advanced level. A roll of empty fire hose with a diameter of 2.5 inches (estimated weight of 20 kg per 100 feet) placed on the upper back increases the load on the straightened arms by 20 kg (i.e., 28.5% load increase relative to body weight). If the recruit’s weight is 70 kg, the total load on the upper limbs is 64.8 kg while performing the push-up. The weighted push-up targets the shoulder muscles (anterior deltoids) and increases the activation of the stabilizing core muscles. No repetition maximum was suggested, consistent with a previous empirical study [20]. In the Fire and Rescue Academy of Malaysia, the decision regarding the number of repetitions to prescribe is dependent on the experience and creativity of the physical trainer after observing the recruits’ performance ability. Heavy loading can be coupled with short rest periods in circuit training, resistance-based interval training, or high-intensity functional training programs to meet specific physical demands for the desired functional fitness goals [4]. Providing short rest intervals (60–120 seconds) between exercises appears to be a practical strategy that allows recruits to recover enough to achieve greater workloads in the next exercise, leading to improvements in the targeted muscle groups. While firefighter recruits should be trained for the most strenuous scenario they might encounter, they should not be trained as athletes who require explosive power for athletic performance. Thus, we did not explore exercises training upper body power with the intent to move as rapidly as possible through the full range of motion, as firefighting activity relies less on how powerful a muscle is. They rely more on how long the muscles can endure while performing essential heavy tasks at more than 7 metabolic equivalents of task (METs) during a fire period [21]. In Malaysia, a fire period can be as short as 30 minutes for a residential fire and as long as 14,400 minutes for a bushfire [22].
The second frequently reported exercise was jumping jack. The exercise that targets the muscles involved in pushing, pulling, lifting, and dragging. The jumping jack is a simple, whole-body aerobic exercise that involves jumping in place while coordinating the swinging of the arms and legs. This versatile conventional exercise works the lower body (i.e., gluteus maximus, hip flexors, quadriceps, and hamstrings), upper body (i.e., shoulder muscles, including anterior, and posterior deltoid), and abdominal muscles. The intensity can be progressed or regressed depending on the individual’s physical needs by adjusting the jump height or speed. The jumping jack is frequently performed for as many repetitions as possible or is interspersed with other whole-body intensive exercises, such as burpees, squats, and mountain climbers. The benefits of this exercise include developing muscular strength and power of the lower body, improving cardiovascular fitness and burning calories. The development of absolute lower body strength may best prepare firefighters for occupational tasks that require their lower extremity muscles to generate force while pulling hoses, carrying equipment upstairs, conducting forcible entries, and dragging victims to safety [17], [23]. A recent study [24] showed that jumping jacks improved heart rate variability and decreased resting heart rate. This exercise promotes positive adjustments in cardiac autonomic modulation by reducing sympathetic modulatory influence and/or increasing vagal modulatory influence on the heart, thus increasing heart rate variability [25], which is associated with a lower risk of CVD [26].
The jumping jack has an MET rating of 8 if performed at a high intensity [9]. For firefighter recruits, the count of 1, 2, 3, 1 is considered one jumping jack in 2 seconds, for an average of 30 jumping jacks in 1 minute (and 60 jumping jacks for the general population). Employing increments of 30 repetitions for the different intensity levels eases the monitoring of timing and the prediction of how many calories are burned. Using the formula for calculating calories burned per minute [27], in which calories burned per minute = 3.5 × MET × weight (in kg)/200, and the calories per gram of body fat values [28], in which burning 3,500 calories is equivalent to losing approximately 2,200 g of body fat. A 70 kg recruit will burn approximately 9.8 calories per minute, equivalent to losing 6.16 g of body fat, when performing jumping jacks. Burning fat is important for recruits in efforts to attain a lean body mass, which hastens heat loss. This is because lean tissue having higher thermal conductivity than fat tissue [29]. Employing jumping jacks in PT, or even as a disciplinary method outside of PT, is important for maintaining recruits’ lean body mass and their resistance to heat stress in hot environments. A previous study [30] revealed that young firefighters were more likely to gain weight and less likely to lose weight compared to older firefighters. As for the optimal number of jumping jacks, recent recommendations [31] have identified a regimen of 50 to 100 jumping jacks performed 3 to 5 days per week in sets of 10 as beneficial, particularly for bone density, which supports the experts’ intensity categorisation in this study.
Having said this, functional strength is subjective and can be influenced by age-related changes in muscle performance and preceding periods of physical inactivity. The time needed to build the strength of targeted muscles is shorter in people younger than 25 years of age compared to those 30 years of age and older. A possible explanation for this may relate to the involuntary loss of muscle mass (primarily skeletal muscle) that occurs with increasing age due to the depletion of proteins and amino acids as the primary substrate of skeletal muscle maintenance [32]. It has been proposed that decreases in testosterone may decrease muscle protein synthesis, muscle mass and strength [9, 33]. Although the levels of bioavailable testosterone remain consistent until men are in their 30s to 40s, after which they decline by approximately 1.2% per year [34], muscle mass begins to decrease by approximately 3–8% per decade after the age of 30 [35]. This is exacerbated by periods of inactivity, with a rate of 1 kg of muscle mass loss observed over 10 days of physical inactivity and accompanied by a decline in strength ranging from 0.3–4.2% per day [36].
Regardless of age- and activity-related considerations, muscle strength can be developed with the correct training. Although it is important to build an age-appropriate programme under a physical trainer’s guidance to prevent injury, this method is not practical in the Fire and Rescue Academy of Malaysia. In this safety-critical recruitment centre, the objective is to produce functionally fit operation crews who can wear full turnout gear and an SCBA while executing rescue and firefighting functional movements regardless of age-related factors. Although recruits’ range in age from their early 20s to their late 30s, they are treated equally to ensure that within 16 weeks they are physically ready for fire suppression tasks, confined-space rescues, and victim extraction from entrapment in vehicles. Examples of fire suppression tasks include pulling down a ceiling using hand tools, laying out the hose, advancing water-filled hose lines, raising, and climbing ladders, lifting and carrying heavy equipment or victims, and conducting search and rescue in a confined area while wearing full turnout gear with an SCBA. The Jaws of Life, a hydraulic rescue tool that is used to cut through cars to open vehicles’ doors and release trapped victims, may be as heavy as 18 to 25 kg. Significant functional upper body strength, dexterity and control are thus needed to manoeuvre the large device around a vehicle.
Overall, the experts prioritised exercises that concurrently target functional strength and the cardiovascular system. These exercises can be easily incorporated with limited equipment in large group settings. While PT programmes improve functional strength levels and job performance in firefighter recruits, PT is just one component of optimising physical job performance and must be employed in combination with appropriate nutrition, good hydration, and holistic physical fitness. Adequate daily dietary protein intake is important for preventing muscle mass loss and thus maintaining skeletal muscle performance. An empirical study on firefighters [37] demonstrated that greater protein intake was associated with increased muscle mass but not muscle strength. The research group suggested that protein intake of > 0.8 g/kg was associated with more favourable muscular body composition in male career firefighters. Complementary to protein, micronutrients such as vitamin D, calcium and iron have been shown to benefit skeletal muscle performance. The active form of 25-hydroxyvitamin D activates the cellular synthesis of new proteins that affect muscle cell contractility, proliferation and differentiation and orchestrates balanced parathyroid hormone production, positively affecting skeletal muscle [38]. Appropriate amounts of parathyroid hormone induce muscle anabolism, calcium–ATPase-related activities and adequate energy availability in skeletal muscle. Iron is an additional essential nutrient for functional movement [39], with iron deficiency causing reduced effort tolerance during both low-intensity and brief high-intensity exercise [40], possibly due to a lack of deliverable oxygen to the exercising muscle and limitations in oxidative metabolism in the skeletal muscle. When designing the PT programme in this study, we assumed that all recruits had adequate nutrition, although internal information regarding recruits’ lifestyles from personal communication and recent empirical evidence from a group of career firefighters in a developed country [41] suggest otherwise. We additionally assumed that recruits had enough hydration and recovery, as ample time was provided for drinking during and between exercise and for sleeping.