150 Chapter 7: Training for Mobility Figure 7.11. Glute Bridge Stretching Recommendations and Precautions Research shows that adequate levels of mobility and flexibility are required in order to reduce the risk of certain chronic diseases as well as prevent the loss of ROM associated with prolonged sitting (Starrett, 2015). As mentioned previously, static stretching is best performed as either a separate training session or as part of the cool-down, but not as part of the general warm-up. In terms of flexibility training, the American College of Sports Medicine (ACSM) provides the following guidelines for static stretching (Magyari, 2018): • Frequency: ≥ 3 days per week • Intensity: Held to a position of mild discomfort • Duration: 10-30 seconds per stretch • Repetitions: 3-5 per stretch Although a 10-30 second hold is a great place to start, most experts agree that individuals should gradually increase the hold duration over time. In fact, research shows that a hold duration of 60 seconds was more effective than either a 15 or 30 hold duration in improving hamstring flexibility (Peterson & Rittenhouse, 2019). Additionally, Starrett (2015) recommends hold durations of at least two minutes or until there is noticeable improvement. In some cases, this may mean spending up to 10 minutes in each position. A sufficient hold duration is necessary in order to stimulate the Golgi tendon organ (a proprioceptor located adjacent to the myotendinous junction that detects changes in muscle tension and when stimulated produces muscle contraction) (Figure 7.5), which in turn allows the muscle to relax and lengthen. As previously mentioned, poor flexibility is more likely a factor of CNS inhibition than it is muscle fiber length. According to Page et al. (2010), muscle imbalances are among the top culprits for musculoskeletal pain, especially in the back, neck, shoulder, hip and knee. These imbalances can lead to patterns of tightness and weakness that can compromise joint function. Page et al. (2010) classifies muscles as either tonic or phasic. Tonic muscles are primarily flexor muscles and tend to tighten with age; whereas phasic muscles are primarily extensor muscles and tend to weaken with age. Examples of tonic muscles include the hip adductors, hamstrings, iliopsoas, and piriformis. Examples of phasic muscles include the quadriceps, glutes, and rectus abdominis. To
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