One of the most common obstacles personal trainers face is the need to modify an exercise program during a session.

A good trainer comes to a fitness appointment with a series of exercises for the client to do. However, even the most well-planned program may need to be modified. The key to success is knowing, based on the client’s unique biomechanics and movement patterns, which modifications to make and how to implement them with confidence.

Getting Started: Break Down Movement

Before deciding how to modify exercises during a session, you need to consider the rationale that underlies the program design. If you know how movement has been broken down to build a program, it becomes easier to analyze an exercise during a session and make adjustments. Here are some of the more common ways that trainers break down movement to build an exercise program:

  • Goal-oriented. The aim is to develop a series of exercises that the client will execute over a period of time to reach desired goals.

  • Disease- or injury-driven. The point is to tailor the program to certain limitations or to provide a starting point (e.g., postrehabilitation) for the client. Either way, the program is designed to help manage or overcome an obstacle, and it’s imperative to account for it when choosing exercises and making modifications.

  • Muscle-specific. This can refer to a long-term program that unfolds over time (i.e., periodization) or to each session as an independent entity (i.e., agonist/antagonist muscle groups).

  • Joint action focused. A session might focus, for example, on muscles that insert at the knee to allow for knee flexion and extension.

  • Compound versus isolation training. Isolation exercises are single-joint movements that focus on one muscle group (e.g., a biceps dumbbell curl). Compound exercises use multiple joints and muscle groups (e.g., a lunge). Isolation exercises are best suited for muscle size and strength goals and are also great for beginners, youth, seniors and persons who may have limited motor coordination or who have been injured. Compound movements are good for total-body training, time-limited sessions, functional training, advanced exercisers and athletes.

Program Design

Once you’ve decided how you’ll break down various moves, it’s time to choose the exercises for each session. Developing a sound exercise program for a client is analogous to developing a business plan; you create a blueprint for what you intend to do, while being realistic about factors that will influence what you actually do once you implement the program.

The key is to remember that the program you design is like a rough draft of a term paper—it’s a starting point. Focusing on a few key action areas can guide you step-by-step through the development of a program draft. These initial evaluations are your guide to the client’s biomechanical characteristics and can be an easy way to discover what modifications you need to make during sessions. Before you get started, address these action statements:

  • Scan for structural limitations. These limitations include any type of therapeutic aid or physical challenge.

  • Watch for unusual movement patterns. Unusual patterns include a limp, a sway or other postural deviations that could cause a muscle imbalance.

  • Estimate the client’s age group. This action applies only to youth and older adults. During youth and late adulthood, motor learning factors are present that influence learning and specific exercise capabilities.

  • Look at body weight and mass. Movement biomechanics for everyday tasks are different for an obese person than they are for a normal-weight person (Runhaar et al. 2011). For example, an obese person performs “sit-to-stand” from a chair differently than a normal-weight person (Sibella et al. 2003). The patterns of muscle activation and joint action are different. Although it appears to be the same movement, the dissimilarities are analogous to those between a barbell squat and a wall squat. In other words, the mechanics and workload are not the same.

  • Listen carefully to the client’s stated goals. This is the most important evaluation of all and can deliver valuable information about the client’s biomechanical characteristics. By listening, you learn how your client views his or her body, including its capabilities and limits. For example, an older adult might say she is concerned about chronic low-back pain (CLBP) and wants to feel better. This information alerts you to two potential obstacles: (1) you must select exercises that are both CLBP- and age-appropriate, and (2) you can anticipate that your client will complain of low-back discomfort during exercise and may be timid about performing some of the moves you select. You will need to be prepared with modifications to keep her on task while easing her discomfort.

Program Implementation

The greatest obstacle that trainers face during sessions, particularly with new clients, is that each person has a unique combination of factors—age, disease, injury, exercise history and motor coordination—that determine his or her ability to learn and execute exercises. Simply put, all people differ in what movements they can do.


Young people who have not yet reached skeletal maturation are a unique group, because their bones are still developing. The American Academy of Pediatrics (AAP) recommends strength training for youth (AAP 2001), with minimal load because bones are immature. All exercises should be modified to use light weights. Training may also include body weight–only exercises; however, body weight exercises can be contraindicated for overweight youth. Their extra weight is an advantage when it comes to moving external loads, but it’s an obstacle during popular calisthenic exercises. Therefore, modifications for overweight youth must include eliminating body weight exercises, while not allowing clients to overdo the use of external loads.

Also, youth training should focus on teaching motor skills associated with fitness. You can help youth develop lifetime fitness habits by frequently changing the exercises you choose, both during sessions and for independent training (between sessions), as youth learn best through varied practice (Schmidt & Lee 2011). Popular ways of introducing variety include circuit training and supersetting.


When modifying sessions for adults, the opposite is true. Adults, particularly older ones, prefer consistency. Training methods such as pyramiding work well, as do more advanced training techniques like forced repetitions (for the conditioned client). The key is to take into account the fact that adults learn exercises best when options are minimal.

As people age and become affected by conditions like arthritis, decreased bone density and postural changes, modifications are essential. Arthritis limits range of motion (ROM) and differentially affects joints. Modifications to arthritic programs may include using isolation exercises—to decrease the total number of joints involved—or using partial-ROM exercises.

Clients with decreased bone density are vulnerable to compression forces. It is therefore important to limit forces that act downward on the spine (as in barbell squats).

If posture is swayed or deviated due to age, the program must take muscle imbalances into account. Modifications should focus on rectifying the differences between opposing muscle groups and opposing sides of the body. For example, modifications for a client with stooped shoulders would include a strong focus on strength training for the posterior muscles of the back versus the anterior. This is in contrast to the traditional way of thinking about program design and agonist/antagonist muscles.

Modifications are a part of fitness training. The key is to know when and how to make them for each client’s unique biomechanics, movement patterns and personal preferences.