## 1 Introduction  
Neck and shoulder pain are frequent in the general population and within several occupational groups that are characterized by monotonous work tasks that require the stability of the head and neck in constrained postures [1; 2; 3; 4; 5; 6]. In often male dominated jobs, helmets add to the weight of the head increasing the demands on the neck muscles and a high prevalence of neck pain is reported among e.g., construction workers, helicopter, and fighter pilots [7; 8; 9]. Physical exercise--in particular specific high intensity strength training at the job--has been shown to effectively reduce musculoskeletal pain in the neck and shoulders [10; 11; 12; 13]. In clinical practice, at work sites, and in home-based rehabilitation the use of conventional resistance training equipment, such as mascines or free weight, may not be a possibility, as it requires high financial cost and advanced facilities. Thus, it is important to identify more feasible alternatives that are easy to perform at the workplace and still effectively target muscles in the neck and shoulder regions. One alternative is the use of elastic resistance bands that has recently gained interest, because they are simple to handle, low in cost, and easy to transport. However, with elastic bands, it might specifically for the neck extensor muscles be difficult to add enough external load as resistance to achieve the requested high activity level. To attain this, a special headband has been invented for more specific, but also more complex, elastic band neck exercises. These complex exercises have been applied in training interventions of helicopter pilots [8]. However, the attendance rate was low, which was possibly due to the more complex head band exercises; and, in that study, it was not investigated whether the more complex exercises actually resulted in a higher activation for the specific muscles when compared to the more simple neck exercises, like shrugs and reverse flyes [8; 14]. The aim of the present study was to assess whether simple exercises as compared to the more complex exercises may suffice for sufficient activation of the neck and shoulder muscles. Regarding the level of sufficient exercise intensity in strength training programs, this is often defined as the percentage of maximal voluntary force exerted [15]. In practice, one repetition maximum (RM) weight is often used as reference for the maximal weight that can be lifted in an exercise for a given number of repetitions. Activation levels of >60% of maximal voluntary contraction force (MVC) are generally recommended to attain a physiological effect of resistance training [15]. A higher force per contraction can be performed the lower the number of repetitions per set, e.g., at 1 RM the performed force is close to 100% MVC, decreasing to around 60% MVC when performing 12 RM--depending highly on training status. In well trained persons 60% MVC might be repeated more times, e.g., corresponding to 20 RM. To access the activation level, electromyography (EMG) is commonly used to measure the activity of the specific muscles that are involved in an exercise [16; 17]; the bilateral upper trapezius muscle (mUTR), upper neck extensor muscles (mUNE), and sternocleidomastoideus muscle (mSCM) were the muscle groups included here. In the prevention and treatment of neck and shoulder pain such EMG measurements can ensure that a given mode and intensity of training will activate the target muscles to the sufficient level [18]. In addition, EMG measures allow for exploratory analysis, such as the development of muscle fatigue during multiple repetitions that might be an indicator of the long-term effect on hypertrophy, as well as the reduced perception of pain. The myoelectrical manifestations used as an indication of muscle fatigue is an increase in the amplitude and a shift in the power spectrum towards lower frequencies [19; 20; 21].